I presented the crayon tinted fabric before, the technique for the crayon coloured t-shirt is a little different and it seems to me that you can get more vivid colours with it.
Links:
Crayon Coloured T-Shirt (DIY Estampando una camiseta) (Spanish and English)
via: Stamping a T-shirt / Estampando una camiseta
Here at unikatissima:
Crayon Tinted Fabric