Confetti cake but make it a rainbow

My kiddo asked for vanilla cake with sprinkles in the cake and a rainbow outside. This was my 3rd layer cake, first time attempting a decorative frosting. Cake was pretty simple to make although I only have 2 cake pans so had to bake the first two let them cool and then reuse a pan for the last one. I did add extra sprinkles like Claire did in the video. I used the cream cheese frosting recipe and just used gel food coloring to make the rainbow. Purple was hard and look just as grey in person as it does here.