Wait until you find out there are warm and cool shades of every color. I can't remember guideline for useage (like cool with cool) so not help at all. Now are you throughly confused.

Can't really remember about the exact technique but you can "sponge" a light blue and then a very light blue (or cool tint white) over the original blue but let the original blue show through. One way you pounce the sponge and with the other you scrub (blur the edges). Like the sky with puffs, clouds and blue patches.

Look at Autmn landscape type pictures which include sky for inspiration. (yellows, orange, red, brown, green and blue)

Good luck.