You'll need to reset the color to white immediately above the call to draw vader. It's keeping the color from the end of the previous frame when drawing the image on the next.
Thanks @leafo. I realized this after looking at other examples.
A bit counter intuitive for this behavior to take place. I've set a default color at the end of my draw function so it works now.
In general, everything that you draw should be responsible for setting its own global state - shaders, colors, filter modes, etc.
