Based on my experience:
The white/silver 3M Scotchlite seems to give the most effective and visibile "glow" from wider angles. "Reflexite" or "Conspicuity" tape (like on construction barrels) is great, too, but seems to have a narrower field of vision.

The others are correct that any coloration besides white will reflect less light back. The tape vendors online will show the stats that prove this; colored tapes are less effective. But colored reflective tape is cool looking, so just make up for it by using more.

I think moving reflectors are more effective than fixed ones, because they easily identify you as a vehicle instead of just a mailbox. The "stock" pedal and spoke reflectors are actually excellent for this; anyone who sees their movement can immediately identify you as a bicycle.

I stick small patches to moving surfaces, like: pedals, rims (facing the hub), crank arms. I also stick a big patch to the rear of the fender. I also replaced the rim strips on my fatbike (with cutouts in the rim) with blue reflexite.

I bought a box of these reflective spoke covers and they're actually pretty great. They come in a box of 72; I split them up and used them on every fourth spoke so they covered four bikes.