diff --git a/src/playground/__init__.py b/src/playground/__init__.py
index 2f5c4e0ab..245134070 100644
--- a/src/playground/__init__.py
+++ b/src/playground/__init__.py
@@ -91,7 +91,7 @@ def tap_to_confirm(address, amount, currency):
         f.seek(0)
         ui.display.icon(3, 170, f.read(), _background, foreground)
 
-    yield from ui.animate_pulse(func)  # , DELAY=10000)
+    yield from ui.animate_pulse(func, ui.BLACK, ui.GREY)  # , delay=10000)
 
 '''
 def on_read():
@@ -130,8 +130,7 @@ def homescreen():
     def func(foreground):
         f.seek(0)
         ui.display.icon(0, 0, f.read(), foreground, ui.BLACK)
-
-    yield from ui.animate_pulse(func, SPEED=400000, BASE_COLOR=(0xff, 0xff, 0xff), MIN_COLOR=0xaa, MAX_COLOR=0xff)
+    yield from ui.animate_pulse(func, ui.WHITE, ui.GREY, speed=400000)
 
 def run():
     ui.touch.start(lambda x, y: print('touch start %d %d\n' % (x, y)))
diff --git a/src/trezor/ui.py b/src/trezor/ui.py
index d15638537..4b648323e 100644
--- a/src/trezor/ui.py
+++ b/src/trezor/ui.py
@@ -38,14 +38,20 @@ NORMAL = const(1)
 BOLD   = const(2)
 
 
-def animate_pulse(func, SPEED=200000, DELAY=30000, BASE_COLOR=(0x00, 0x00, 0x00), MIN_COLOR=0x00, MAX_COLOR=0x80):
+def lerpi(a: int, b: int, t: float) -> int:
+    return int(a + t * (b - a))
+
+
+def blend(ca: int, cb: int, t: float) -> int:
+    return rgbcolor(lerpi((ca >> 8) & 0xF8, (cb >> 8) & 0xF8, t),
+                    lerpi((ca >> 3) & 0xFC, (cb >> 3) & 0xFC, t),
+                    lerpi((ca << 3) & 0xF8, (cb << 3) & 0xF8, t))
+
+
+def animate_pulse(func, ca, cb, speed=200000, delay=30000):
     while True:
-        y = 1 + math.sin(utime.ticks_us() / SPEED)
-
-        # Normalize color from interval 0:2 to MIN_COLOR:MAX_COLOR
-        col = int((MAX_COLOR - MIN_COLOR) / 2 * y) + MIN_COLOR
-        foreground = rgbcolor(BASE_COLOR[0] + col, BASE_COLOR[1] + col, BASE_COLOR[2] + col)
-
-        func(foreground)
-        yield loop.Sleep(DELAY)
-
+        # normalize sin from interval -1:1 to 0:1
+        y = 0.5 + 0.5 * math.sin(utime.ticks_us() / speed)
+        c = blend(ca, cb, y)
+        func(c)
+        yield loop.Sleep(delay)