How to deal with a bad haircut or the wrong colour hair before an audition
For most acting jobs your hairstyle is very important, particularly screen work. If you have been invited to audition for a piece set in the 1950s (for example) then your hair can really aid your audition if you choose to style it in a cut/style that was popular at the time. Some hairstyles can be achieved with a simple application of gel or spending some time with hair straighteners/curling tongs, and, providing you have these items, you won't be out of pocket for adding that little extra addition to your overall appearance in relation to the character.
If you feel you have a bad haircut or your colour hair dye limits your ability to style your appearance on a range of characters then it's probably time for a haircut. It is important to find a good hairdresser/barber that understands your needs and is good at what they do, so if your hairdresser/barber isn't very focused on style and getting the best out of their skills then have a look around for better, more reliable hair professionals. You may end up spending more than you'd like on your hair but your overall image is extremely important in selling yourself so you need to see it as a necessary expense for your business.
Hairdressers/barbers tend to be very chatty and show an interest in their clients (good ones anyway) so tell them about your career and let them know how vital your hairstyle is in what you do so they can expect that you'll be wanting to change your style occasionally to match jobs/auditions.
You don't need to go extreme in hairstyle changes, particularly if it's for an audition and not a job. You need to keep your overall image consistent (unless you're happy to pay for new headshots each time you get a haircut). Always check with employers before getting your hair cut because they may wish for your hair to remain as it was when they first saw you or they may have plans for their own stylist to do it.