Hi there this is the first in a series of 5 step tutorials that should help painters who struggle with certain colours or details of paining.
For painting blue you’ll need the following items:
Regal blue
Midnight blue
Enchanted blue
Bleached bone
Skull white
Chaos black
Scorched brown
I’d also recommend using fine brushes say sizes 2 to about 00, I’d say these are the best size for most models.
Stage 1: paint a mix of 30% midnight blue, 40% regal blue, 10% chaos black and 20% scorched brown. With this mix cover the entire area you want to paint blue. I recommend that you do two or three thin coats instead of one thick one.

Stage 2. Now with that area dry mix ; 80% regal blue, 15% scorched brown and 5% chaos black. Paint this over 80% of the base coat or just so you can see the original coat in the lower parts of the model.

Stage 3. Now the darker areas of the model are done you can move on to the main areas. For this mix; 50% regal blue and 50% enchanted blue. Paint this over 80 % of stage 2.

Stage 4. Now mix; 30% regal blue, 55% enchanted blue and 15% bleached bone. Paint this in thinner coats than you have been doing over 50%-60% of stage 3

Stage 5. Finally add some skull white to the stage 4 mix and highlight 20% of stage 4. After this I recommend you use a few layers of thinned blue ink.

And that’s it simple and quick tutorial for blue. If you have any questions please pm me.
Hope this has helped
All the best
Zain.