Voices Question

I notice that whenever I need a second voice and press control + v a little plus sign and a number appear under the stave. What does this mean?
Can I change the color of each voice?

Under the View menu, select Note Colors -> Voice Colors (I don’t think they print). The online documentation for voices is here: https://steinberg.help/dorico/v1/en/dorico/topics/write_mode/write_mode_voices_c.html