AH! Today's episode made me so happy. I realize that he very well could be Rainbow's older brother or something like that, but in my head-canon, its her dad. And in the past I've wanted to draw her parents before, and today seemed like a good a day as any, especially with a male rainbow-maned pony revealed today.
(Also, what the heck was his cutie-mark? It looked, to me, like a pony's legs or a butterfly-cloud with a rainbow streaming behind it.)
I dub her dad Spectrum Blast and her mother Sun Prism. Just a bit of story-idea-storming. Her dad was the head of the Cloudsdale weather control. Sun Prism was a member of the Wonderbolts, but while Rainbow was still young she died or went missing on a mission or something that removed her from Rainbow's life. Spectrum was a great dad and worked hard to teach Rainbow to be the best flyer ever and told her stories of her mom's Wonderbolt adventures often. From that, she gained her dream to become a Wonderbolt someday like her mother. Yeah... Something like that.
Also also, I realize that Spectrum's head might be too small, but I took too long on this as is, and I have 2 oil paintings to finish due Monday.