There are two kinds of knobs on the matrixbrute: white and gray. Its unclear why the white knobs are white. Maybe because they are somewhat performance related?
It may be an idea to use the two colors for another purpose, to separate those that can be controlled from the matrix from those that cannot.
As far I can see the only knobs that cannot be assigned to the programmable Matrixrows are
the main volume and headphone output knobs
The knobs in the sequence group : rate, swing and gate
They could be made white in future versions
It's a real pity that the sequence rate knob cannot be assigned to the Matrixrow. Imagine being able to control the speed of the sequences with an envelope or with the single phase option of LFO1....
On second thought is is very strange that sequence rate cannot be assigned to the matrix, because the speed can be controlled with continuous Controller 15 according to the manual and the other knobs in the sequencer section with CC 17 and 18. Is this an oversight?