1
The playroom is painted with warm colours.
The playroom is painted in warm colours.
Use painted in + colour/colours when describing the colours of a room or object. The purple sentence is possible, but it focuses more on the colours or paints used.
2
All the rooms are painted in white colour.
All the rooms are painted white.
When a colour word directly describes something, do not add colour: a red car, a blue jacket and walls painted white.