[ilikexd]

it's ok to use color notes for an unquantized or offbeat solo

it's not ok to have a color file because you haven't figured out the bpm

ddream is easier for syncing tracks with dynamic bpm, but both sm and ddream can do it
it's as simple as placing the beats on the downbeats in the music
for some genres like rock where the tempo is being set by a drummer, it usually has a clear kick or snare visible in the filtered waveform in ddream to which beats can be aligned
the truth is it just takes lots of time and practice to actually train your ears and improve your hearing to get better at syncing

you should, in my opinion, wait until you are proficient at stepping music with a static bpm before trying music with dynamic bpm as it'll be even further error-prone and unnecessarily difficult