I agree with what most have said here -
and notice that visibility in the sky going up, going down, and on the ground- all have some opposing criteria-
The worst situation is probably a small rocket against cloud or overcast sky. Those sidewinders with the scale light gray paint job disappear instantly!
Dark colors on the airframe with some sparkly reflective areas seem to work best for going up. Fluoresecent orange seems to work best around here against vegetation or dirt.
Going down its usually the chute/streamer that counts the most. If there's any sun out, a streamer made from 'holographic' metallic gift wrapping mylar film, (3 for a dollar) does a great job of sparkling in the sun and helps a lot with smaller or less visible chutes. I've even made 'Estes'-style chutes from the stuff, up to 3' dia.
One trick i've thought of and will try this season for some min-dia. birds is to paint one side a dark color (say flat black) and the other side a bright sparkly one ( fluorescent orange with a metallic stripe) with fins not quite straight so it has a slow spin, the alternating flash of light and dark should make it especially visible in the sky going up.
One other thing i've always wanted to try, if the airframe is big enough: include a small helium "saussage" balloon with a 30' kite string in with the chute (longer for wooded areas). trick is finding a way to protect it from being popped at ejection.
If it works, you end up with a perfect "I'm over here!" marker floating high above the landing spot.
We often launch around corn fields that seem to have a magnetic attraction for rockets, especially in the fall when the corn is 8' tall. spotting anything in there from more than 10 feet away is nearly impossible.
Under these circumstances (also good for hilly terrain/brush) i've gotten in the habit of attaching a long piece of bright red "danger" tape or similar streamer material- at least 30'-50' long- to the shock cord. it helps in the corn because it gets caught and stays near the tops of the stalks/bushes even if the rest falls to the ground between the plants, and thus helps you see it from further away as you're trudging up and down the corn rows. A beeper is also a huge help here.
Instead of plain G4 for fins, i often use surplus circuit board material, with a thin film of copper laminated to both sides. with some 4f steel wool and a little elbow grease, it takes a high polish very quickly, and a quick spray of clear urethane helps keep it that way. if the sun is out they flash very brightly and can be seen for miles.