I broke down and colored my hair last week. It won't fall out from regular coloring (highlighting might weaken the hair enough to break off if its left on too long) but the real issue is how much of the chemicals are absorbed in your scalp and affecting your liver. I decided I was getting depressed looking in the mirror at my drab hair and thought it would be healthier for me to color it and make me happy than to abstain. This is week 29 for me and my hair has been shedding at a rapid rate for 9 weeks but looks OK so it isn't bothering me any more.
Highlighting isn't usually touching the scalp and should be fine if you are in a well ventilated room. Hope this helps.
Dot
This is a recurring question for all of us women. As a hairdresser for almot 30 years, I feel qualified to answer. I could and will get technical for anyone who wants me to (regarding epithelial cell generation, etc) but the basic answer is, yes you can color your hair. I would avoid rough handling (whether on tx or not!) over vigorous brushing, 'baby' shampoos which are harsh due to a high pH, and probably perms which stress the entire strand and folicle. Double process bleaching is likely to be a no-no, too. Most of us seem to report the most drastic thinning at about week 18-24. After that, things seem to settle down but the scalp, along with the skin on the rest of our bodies can go apeshit. At 11 months post-tx my hair is shiny again and is back to pre-tx thickness. Try not to worry too much. Just get through tx and try not to over-stress yourself about stuff you can't change for now.
I noticed my hair thinning around week 20. I'm now wk 44 and I don't notice it any longer. I have had highlights done every other month the whole time on tx. Doesn't seem to have done any harm.
I used to have a lot of body and some curls; since on tx my hair is now very straight and baby fine so the color gives me a little body for awhile.
Good luck to you.