While I agree with you on point 1, Alison is less desperate finally getting her school crush (Ian and Alison liked each other in school already, but never acted on it), I think there is more to the hairdye than just one variable.It's not a punishment. It means she feels more secure/less desperate so she feels comfortable asking him to wear the condom.
Same reason that she doesn't dye her hair if you are on her love route.
I have two Alison love route saves, one pure love from the start, one pure love route but with the Jeremy threesome. In the one with the threesome (Ian being a stud here) Alison still colours her hair and I could gain her blond version with the love route from the start once.
I think while the "love meter" has some influence here, how "hot" you consider Lena and Sherry (and if Alison knows this) also plays a role.