OFX Transition Plugin

I’m creating a transition that lets you select various blend methods. I’ve got it mostly working, but I’m unable to keep rgb values within 0.0 and 1.0. If I have no color correction on the two clips or disable CC nodes, the blend methods work as expected, but if I do some CC, such as lowering shadows below 0, the effects act as if they are being passed negative numbers or numbers greater than 1. I tried clamping the source video levels and/or the destination levels to between 0 and 1, or 0.00001 and 0.99999 but it doesn’t help. How do I keep levels sent to my effects between 0 and 1?