How to assign constant value to closure color?

Syoyo Fujita <syoyo...@...>

What is the best way to assign constant value for closure color variable?

For example, I'd like to write a shader such like this.

Ci = color(1, 0, 0);

Unfortunately, as spec 5.10 says, we cannot assign color value to
closure color, thus the above expression cannot be compiled by oslc.