Are you talking about showing colored signals on a waveform? Or use $display()-like function to print colored text to the console?
In case you are asking about signals, you can use `-color` parameter when adding a signal to the wave, for example:
add wave -label "value" -radix unsigned -color orange /dut/value
add wave -label "valid" -color orange /dut/valid
If you are talking about $display, then I guess it depends on the OS you are using and how you run the ModelSim. For example, on Linux in console mode, you can do something like this:
$display("\033\033[0m");
I run the simulation like this:
$ vsim -c -do ./mysim.do
... and see a green-colored "[OK]" in terminal (screenshot attached).
