Genetics of Zea Mays (maize)

Hi, I'm doing some biology homework on genetic variation, and I'm kinda stuck!

Well so the case is this:

Maize plants that were grown from purple grains had cobs that had all purple grains. When fully grown, the resultant plants were self pollinated, giving these results in the cobs produced:

Purple grains: 1836

Red grains 578

White grains 772

I have been given a hint that the alleles are: R - red, r - colourless, E - purple, e - colourless, and am supposed to draw a genetic diagram to show the cross described...

From the ratio of purple:red:white grains, I'm pretty sure it is recessive epistasis, yet i'm not sure of the relationship between the alleles given in the hints.

Could someone point me in the right direction, please?

Thanks in advance!

Cheers.