Try to assign any Renderman shader to the light and change the color of light inside the RIB tab. It's impossible (but the trick with MMB still exists).

The light color setting on the Light Object is for when you don't have a SHOP applied. When you have a SHOP applied, RenderMan or VEX, you need to control the color through the SHOP.

Its quite common for people to make Light Assets which have the SHOPs buried inside the asset. This allows you to have a single interface for lights, instead of having to manage the transform on the Light Object and the shading parameters on the Light SHOP.

Anyway the interface has the bug

hoknamahn
Anyway the interface has the bug

What version are you using? Seems to work fine with 8.1.810.

8.1.733

Hey wolfwood. It doesn't work in 8.1.851 too.
Try to do step by step:
Light->Illumination->RIB->RIB Shader->sliders->pickup the color.
Seems that Dialog Script window is modal.

Modal indeed. That RIB Shader interface is ancient and AFAIK is just there for backwards compatibility, its best to use SHOPs instead. I wouldn't be surprised if it disappeared within the next couple of versions of Houdini.