in shimmer/src/main/java/com/facebook/shimmer/Shimmer.java [353:357]
public T setBaseAlpha(@FloatRange(from = 0, to = 1) float alpha) {
int intAlpha = (int) (clamp(0f, 1f, alpha) * 255f);
mShimmer.baseColor = intAlpha << 24 | (mShimmer.baseColor & 0x00FFFFFF);
return getThis();
}