lightening colors on clothing for direct sun use

It depends on the fabric you are considering. It's a lot easier to do with natural fabrics, but for synthetics the color seems to more deeply embedded into the fiber. I'm not sure, but i think they add the dyes into the plastics when it's in a more plastic malleable state before they extrude it?

In any case, i've tried to lighten up a garment which had both synthetic and natural fibers in it, and you could see that the natural fibers did lighten up some, but the synthetic ones didn't change appreciably, and so the overall color didn't lighten up that much. (the ratio of natural to synthetic fiber was about 50/50).

Re: natural fibers, don't ever subject wool to common bleaching processes, especially the high ph kinds like bleach or oxi-clean–these will rather quickly degrade and almost dissolve it. An acid based bleaching agent would be much better, i "think". Maybe something like lemon juice?

"I'm not sure, but i think they add the dyes into the plastics when it's in a more plastic malleable state before they extrude it?"

Did some more research into this, apparently the above is only true of polypropylene. Disperse dyes are often used with polyester. Nylon apparently can be treated both with disperse dyes or acid dyes that work on wool and other protein fibers. Interesting…

So, if your garment is polyester or nylon, they sell a color lightener at Joann's fabrics–it's near the RIT dyes in a pink box.

Having tried it once so far, i recommend using the stove top method if you really want to lighten it up. I used one packet and did the machine wash method–somewhat against the instructions (they say two packets for machine wash method vs 1 for stove top). I noticed noticeable lightening of the garment, but not as much as i wanted. Going to treat it again. Went from cocoa brown to a mid brown–hoping to get it closer to a lighter tan.

Side note. Bloody polypropylene though. Don't think my silver method is going to work with this stuff, alas. The irony of it, the garments that most needs to be treated with silver.