Midi lauchpad rarely supports full rgb. Usually, it's more like each button is controlled like a color wheel attribute. The exact midi values the launchpad is expected should be in the user manual.
Alternatively, pacth a generic dimmer for the proper midi note or cc as expected by the lauchpad. It's usually the same midi message that is sent that is expected for the midi feedback.
Then try various values for the dimmer. Also make sure to enable the midi output for your launchpad in Lightjams. Go in thr view/configuration and under the midi tab.