Formal:
* J'ai des murs roses et lilas. (This is the most direct and literal translation)
Informal:
* Mes murs sont roses et lilas. (This translates to "My walls are pink and lilac")
* J'ai des murs couleur rose et lilas. (This is similar to the formal option, but emphasizes the color)
You could also be more specific with the shades of pink and lilac, for example:
* J'ai des murs rose pâle et lilas clair. (Pale pink and light lilac walls)
* J'ai des murs rose fuchsia et lilas foncé. (Fuchsia pink and dark lilac walls)
The best option depends on the context and your level of formality.