I need to paint a small patch of my bathroom ceiling.  I appreciate I may not get an *exact* match.  The ceiling is white, plain and simple white.  I have tried two different paints, one was called cotton socks white and the other one is something like brilliant white.  They look blue on the ceiling, white on the packaging and from the pot.  How do I buy white paint?  Does it need several coats before it turns white?  I put some sealant underneath it but the sealant is whiter than the paint.
 
Thank you, DIY experts.
 
(May resort to Tippex)