Do I need to undercoat the walls first...? Decorating advice needed

[runner2]

The walls are currently a deep-ish lilac colour and I've got a Dulux deep blue to paint over it. Should I do a white emulsion coat first or can I be confident a couple of coats of the blue will cover it?

I would go straight for the blue. I only undercoat when painting on new plaster for a mist coat*

*not a professional

Test it an find out....I would think you will struggle to get the true colour tho....what finish is it?

I would do a test patch both ways and compare how true the colour is.

Do two coats of the blue. If it doesn't cover it, do a third coat. I wouldn't have thought a dark colour would have much trouble covering another dark colour, normally the trouble comes when you want to put a light cover over the dark.

It's a Dulux matt emulsion to cover a silk (ie slightly shiny) finish. Think I'll just do the couple of coats and hope that's enough...

You will get the true colour if you paint over white paint

You may not like the colour if you paint over what you currently have

As previous people have said the best thing to do is test it out first

Even putting dark blue over white can need a third coat to get the full depth of colour, so I would just try two coats straight over the purple and see what it comes out like. Then do a third if you think the blue doesn't have the full depth of colour.