My roommate washes her hair EVERY day and always blow dries and flat irons every day as well. Her hair has never been colored though.. but her hair is very healthy. If I straighten mine, I'll skip a day, but when I don't straighten it, I usually wash it every day. I think you just have to see what works for your hair. If you hair is oily, it can handle more washing a lot more than somebody with dry hair. I had damaged hair about 1/2 a year ago and could go probably like a week and my hair wouldn't even feel oily at all.
With the highlights, using some shampoos can fade the color or make it brassy. Salons suggest using products made for color treated/highlighted hair. They make lavender colored shampoos that are good for keeping blonde highlights from going brassy. If yours fade, you can try some of those out, but if they don't, then you are just lucky!
If you are concerned and notice any damage in your hair, they make hair powders that absorb any greasy oily at the roots so you can skip a shampoo without feeling gross. However, if your hair looks good and is healthy, then you might as well keep doing as you do! If you have strong hair, you must be doing it all right for yourself

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