Add trichromatic/monochromatic toggle to the "Grain" Adjustment Layer, just like the "Add Noise" Filter

You’re right, the adjustment layer is Luminance noise only. To be realistic, it needs about 30% color noise.

I’m pretty happy with the texture itself. It can be made to mimic sensor noise quite well (don’t know about analog film grain, haven’t seen that for a long time...). In any case, it’s much better than Add Noise, which always needs a little extra blur. Here that isn’t necessary. But there needs to be a color component - an extra slider would be ideal.