OK to bundle wires together with colored electrical tape?
It's mandatory

When putting identical-appearing circuits in a conduit, you must differentiate them somehow.  It's mandatory. 

I would not bundle them but mark them individually.  Black(blue) and White(blue) for instance being the obvious pair. Bonus points: use a decent length (2") of shrinkwrap so the tape doesn't come off someday. 

The reason I don't like bundling them is pulling. It will make pulling harder by making wires bind.  

Get rid of those grounds

Grounds don't count against wire-size derate (on 10, 12, 14 AWG you are allowed 9 active conductors per conduit without worrying about derate). Having considered this math in every way possible on 120/240 split-phase, this means 4 circuits of any kind. 

But they do count against conduit fill - in 1/2" EMT you are allowed 9 wires fullstop... and you are now full.  Dump two of the grounds and you will be able to fit a fourth circuit.  Use the 10-32 ground screws in the boxes to splice grounds.

EMT itself is a ground path. One ground in EMT is belt-and-suspenders.  Three is inexperience.  The only reason to pay the fill cost for that is if you were splitting the circuits into nonmetallic conduit downline, and the split point lacked any place to splice the grounds - I have had to do that.