fix(workflows): preserve contrast on gradient tiles

apps/sim/blocks/icon-color.test.ts

@@ -18,9 +18,10 @@ describe('isLightTileColor', () => {
     expect(isLightTileColor('#B2C147')).toBe(false)
   })
 
-  it('treats dark tiles, gradients, and empty values as dark', () => {
+  it('uses gradient stops while keeping dark and empty values dark', () => {
     expect(isLightTileColor('#171717')).toBe(false)
     expect(isLightTileColor('#9B5CFF')).toBe(false)
+    expect(isLightTileColor('linear-gradient(180deg, #E0F7FA 0%, #FFFFFF 100%)')).toBe(true)
     expect(isLightTileColor('linear-gradient(45deg, #fff, #000)')).toBe(false)
     expect(isLightTileColor(null)).toBe(false)
     expect(isLightTileColor(undefined)).toBe(false)

apps/sim/blocks/icon-color.ts

@@ -4,7 +4,7 @@
  * these without pulling 282 block configs and the tool registry into its bundle.
  * Registry-backed icon styling lives in `@/blocks/brand-icon`.
  */
-import { isLightColor } from '@/lib/colors'
+import { perceivedBackgroundBrightness } from '@sim/utils/color'
 
 /**
  * Brightness above which a brand tile is "clearly light" and a white foreground
@@ -18,11 +18,12 @@ const LIGHT_TILE_THRESHOLD = 0.75
 
 /**
  * True when a block's {@link BlockConfig.bgColor} tile is light enough that a
- * white foreground icon would wash out. Gradients and unknown values are
- * treated as dark (the common case for brand tiles).
+ * white foreground icon would wash out. Gradients use the average brightness
+ * of their supported color stops; unknown values are treated as dark.
  */
 export function isLightTileColor(bgColor: string | null | undefined): boolean {
-  return Boolean(bgColor) && isLightColor(bgColor as string, LIGHT_TILE_THRESHOLD)
+  const brightness = bgColor ? perceivedBackgroundBrightness(bgColor) : null
+  return brightness !== null && brightness > LIGHT_TILE_THRESHOLD
 }
 
 /**

packages/utils/src/color.test.ts

@@ -1,5 +1,5 @@
 import { describe, expect, it } from 'vitest'
-import { perceivedBrightness } from './color'
+import { perceivedBackgroundBrightness, perceivedBrightness } from './color'
 
 describe('perceivedBrightness', () => {
   it('returns 1 for white and 0 for black (hex and keywords)', () => {
@@ -27,3 +27,31 @@ describe('perceivedBrightness', () => {
     expect((perceivedBrightness('#3B82F6') as number) < 0.6).toBe(true)
   })
 })
+
+describe('perceivedBackgroundBrightness', () => {
+  it('preserves solid-color brightness', () => {
+    expect(perceivedBackgroundBrightness('#ffffff')).toBe(1)
+    expect(perceivedBackgroundBrightness('#000000')).toBe(0)
+  })
+
+  it('averages supported CSS gradient stops', () => {
+    expect(
+      perceivedBackgroundBrightness('linear-gradient(180deg, #E0F7FA 0%, #FFFFFF 100%)')
+    ).toBeCloseTo(0.9715)
+    expect(perceivedBackgroundBrightness('linear-gradient(45deg, #000, #fff)')).toBe(0.5)
+    expect(
+      perceivedBackgroundBrightness('radial-gradient(circle, black, #fff, white)')
+    ).toBeCloseTo(2 / 3)
+  })
+
+  it('returns null for unsupported backgrounds', () => {
+    expect(
+      perceivedBackgroundBrightness('linear-gradient(45deg, currentColor, transparent)')
+    ).toBeNull()
+    expect(
+      perceivedBackgroundBrightness('linear-gradient(45deg, #fff, rebeccapurple, #000)')
+    ).toBeNull()
+    expect(perceivedBackgroundBrightness('linear-gradient(rebeccapurple, #fff, #000)')).toBeNull()
+    expect(perceivedBackgroundBrightness('currentColor')).toBeNull()
+  })
+})

packages/utils/src/color.ts

@@ -20,6 +20,64 @@
  */
 export function perceivedBrightness(color: string): number | null {
   const value = color.trim().replace(/['"]/g, '').toLowerCase()
+  return parseSolidBrightness(value)
+}
+
+/**
+ * Perceived brightness of a solid color or static CSS gradient background.
+ * Gradient brightness is the average of supported hex/black/white color stops,
+ * a small deterministic heuristic for choosing readable tile foregrounds
+ * without a browser color parser. Unsupported backgrounds return `null`.
+ */
+export function perceivedBackgroundBrightness(background: string): number | null {
+  const value = background.trim().replace(/['"]/g, '').toLowerCase()
+  const solidBrightness = parseSolidBrightness(value)
+  if (solidBrightness !== null) return solidBrightness
+
+  const gradient = value.match(/^(?:repeating-)?(linear|radial|conic)-gradient\((.*)\)$/)
+  if (!gradient) return null
+
+  const [, gradientType, contents] = gradient
+  const parts = contents.split(',').map((part) => part.trim())
+  const firstStop = parseSupportedColorStop(parts[0])
+  const colorStops = firstStop === null ? parts.slice(1) : parts
+  if (
+    colorStops.length < 2 ||
+    (firstStop === null && !isSupportedGradientPreamble(gradientType, parts[0]))
+  ) {
+    return null
+  }
+
+  let totalBrightness = 0
+  for (const colorStop of colorStops) {
+    const brightness = parseSupportedColorStop(colorStop)
+    if (brightness === null) return null
+    totalBrightness += brightness
+  }
+
+  return totalBrightness / colorStops.length
+}
+
+function parseSupportedColorStop(value: string): number | null {
+  const match = value.match(/^(#[0-9a-f]{6}\b|#[0-9a-f]{3}\b|(?:white|black)\b)(?:\s|$)/)
+  return match ? parseSolidBrightness(match[1]) : null
+}
+
+function isSupportedGradientPreamble(type: string, value: string): boolean {
+  if (type === 'linear') {
+    return /^(?:-?(?:\d+(?:\.\d+)?|\.\d+)(?:deg|grad|rad|turn)|to\s+(?:top|right|bottom|left)(?:\s+(?:top|right|bottom|left))?)$/.test(
+      value
+    )
+  }
+  if (type === 'radial') {
+    return /^(?:(?:circle|ellipse|closest-side|closest-corner|farthest-side|farthest-corner|at)\b|-?(?:\d|\.\d))/.test(
+      value
+    )
+  }
+  return /^(?:from|at)\b/.test(value)
+}
+
+function parseSolidBrightness(value: string): number | null {
   if (value === 'white') return 1
   if (value === 'black') return 0
   const hex = value.replace('#', '')

packages/workflow-renderer/src/lib/tile-icon-color.test.ts

@@ -0,0 +1,13 @@
+import { describe, expect, it } from 'vitest'
+import { isLightTileColor } from './tile-icon-color'
+
+describe('isLightTileColor', () => {
+  it('detects light gradients that need a dark foreground', () => {
+    expect(isLightTileColor('linear-gradient(180deg, #E0F7FA 0%, #FFFFFF 100%)')).toBe(true)
+  })
+
+  it('keeps a light foreground on dark and mixed gradients', () => {
+    expect(isLightTileColor('linear-gradient(45deg, #4D27A8 0%, #A166FF 100%)')).toBe(false)
+    expect(isLightTileColor('linear-gradient(45deg, #000, #fff)')).toBe(false)
+  })
+})

packages/workflow-renderer/src/lib/tile-icon-color.ts

@@ -1,4 +1,4 @@
-import { perceivedBrightness } from '@sim/utils/color'
+import { perceivedBackgroundBrightness } from '@sim/utils/color'
 
 /**
  * Foreground class for a brand icon rendered inside its colored block tile.
@@ -18,6 +18,6 @@ const LIGHT_TILE_THRESHOLD = 0.75
 
 /** Whether a provider tile needs dark foreground content for legibility. */
 export function isLightTileColor(bgColor: string | null | undefined): boolean {
-  const brightness = bgColor ? perceivedBrightness(bgColor) : null
+  const brightness = bgColor ? perceivedBackgroundBrightness(bgColor) : null
   return brightness !== null && brightness > LIGHT_TILE_THRESHOLD
 }