i don't see that option on the gauge. In case you are doing a horizontal gauge, you can easliy convert that to a bar chart.
When you do this enter a synthetic dimension for the bar (the gauge requires no dimension). Something like this:
The measure would stay the same.
Then open up appearance and you'll have the ability to switch it to a vertical or horizontal bar AND color by Expression. You can use a lot of color funcitons in the expression. Here is something basic: