Here comes the Lilac description from my book written by a Dutch known breeder:
A perfect Lilac: Evenly coloured, no differences in colour, except for the belly side. There it has to be a bit less "brightly coloured" (thump?).
Lilac looks to have a light blueish colour with a pinkish glow. The picture that is shown has a cavy which looks light gray with a strange twist.
Ears and the flesh under his feet (sole?) have to be flesh-coloured, nails have to be "horn-coloured". Eyes are always red.
A perfect Beige: Dark cream-coloured with a greyish haze, may not look brownish. Evenly coloured, no other colours may be present. The rest is the same as the lilac race. A beige cavy could be best describes as bleached lightbrown.
The book notes that the breeding of the right colour for lilacs is extremely difficult and that between Lilac and Beige holds some kind of relationship to each other.
If I compare the two photo's in the book, I would say he looks much more like a lilac than a beige. Your cavy also carries a brownish glow it seems. maybe it is the relationship the book told about. Still I think it is a Lilac-like cavy more than a Beige one, because beige is simply a different colour. I wish I had a scanner, so I could show you the pictures.