Add color blending func

dachlatten-compose/src/main/kotlin/de/sipgate/dachlatten/compose/color/blend.kt

@@ -0,0 +1,18 @@
+package de.sipgate.dachlatten.compose.color
+
+import androidx.compose.ui.graphics.Color
+
+fun blend(
+    color1: Color,
+    color2: Color,
+    ratio: Float,
+): Color {
+    val inverseRatio = 1f - ratio
+
+    val red = color1.red * ratio + color2.red * inverseRatio
+    val green = color1.green * ratio + color2.green * inverseRatio
+    val blue = color1.blue * ratio + color2.blue * inverseRatio
+    val alpha = color1.alpha * ratio + color2.alpha * inverseRatio
+
+    return Color(red, green, blue, alpha)
+}

dachlatten-compose/src/test/kotlin/de/sipgate/dachlatten/compose/color/ColorTest.kt

@@ -0,0 +1,16 @@
+package de.sipgate.dachlatten.compose.color
+
+import androidx.compose.ui.graphics.Color
+import org.junit.jupiter.api.Assertions.assertEquals
+import org.junit.jupiter.api.Test
+
+class ColorTest {
+    @Test
+    fun equalPartsOfRedAndBlueResultInPurple() {
+        val red = Color.Red
+        val blue = Color.Blue
+
+        val result = blend(red, blue, 0.5f)
+        assertEquals(Color(128, 0, 128), result)
+    }
+}