Correct it is red.
My tree says it has 4 prereqs
The research tree says I have done all those prereqs. However an old blueprint from V1.1 shows the portable reactor and Exoskeleton as not available to build. Big Red circle with a line across it. I think it is one of the mods I am using causing this ...

Well I have completed all the research except for the ones you can just keep doing and still cannot start the spidertron research. Must have a bug of some kind.

I have researched everything up to Spidertron and all the dependencies are complete but it will not allow me to research the spidertron. I have Military 4, Spiderling, Nuclear Power and Efficiency Module 3 which are the 4 above it.
Why won't it allow it? Have checked the tree and they are all green ...