Unfortunately this requires an insane and unhealthy amount of hair stripping and dyeing so wigs really are the way to go. However, if you feel like pastel is more the look you're going for, I have the solution for you!
Yup. Good old fashioned sidewalk chalk is a quick easy temporary solution. Take the color you want, soak it in a bowl of warm water for a a few minutes to soften and saturate the chalk (the longer it soaks, the more vibrant the color will be - up to 15 minutes) and then color over your hair.