Can painting on silk and matt cause paint colour to be different?

Natty2310

I've started decorating our flat, and I'm no pro to painting as never had to do it before. I just know the general stuff.
Our bedroom has two different coloured paints on it (2 walls cream, 2 walls a dark blue/green colour). I've used a tester paint to check the colour that it would come out as on the walls and the paint is coming out a completely different colour on the different coloured walls. I know it's not due to lighting because it's a well lit room and the lighting is the same throughout.
I have noticed that the cream paint on the walls is cracked, does that mean the previous tenants have painted a matt paint on top of a silk paint? And the blue/green colour is quite shiny, so I'm guessing that's a silk paint? Can a colour on top of a matt paint look a different shade to a colour on top of a silk paint?

Thanks for any help!

brightontraveller

Normally just painting over a darker colour with lighter you will notice a difference?
Give all walls an appropriate rubbing/sanding down for an effective key. Then 1 or 2 coats of contact matt white or a light grey undercoat. (Obliterate darker colour underneath) Then two coats of emulsion painting in general is better done in natural lighting than artificial?

Cracking could be a number of things ditto previous paint if it is silk as long as you sand it enough should be ok