While I'm not a genetics expert, I have learned a thing or two in the last 10 years of managing my olive egger flock and line breeding back to get the Barnevelder double laced gold.
First, congratulations on your roo and good luck to your future endeavors. Now some genetics.
This is a good resource to begin to simply wrap your head around basic chicken genetics:
https://scratchcradle.wordpress.com/genetics-mini-series/
It begins with egg color, as that really is the simplest of genetic traits (except brown is pretty complicated...taking 13 genes to juggle to keep dark brown, which I've learned is rather hard). It advances through other traits. Easy reading overall. Good resource.
I also recommend simply running your bird types through the gene calculator. (2nd tab down is English, as you will see) There is a lot of genetics information on the website. Some of it pretty complicated, so pick through it slowly. I gave you the direct link to the genetic calculator. Put in your color type for rooster and hen to see results. (Your rooster is likely Dominant White, your Cuckoo Marans Barred/Cuckoo, your Andaulusian and others Blue, etc.)
http://kippenjungle.nl/Overzicht.htm
Basics from Kippenjungle:
http://kippenjungle.nl/basisEN.htm
Finally, an old standby which is in public domain. Good for line breeding discussion (when to breed offspring back to parents to set traits). It's a bit old timey in vocabulary, but worth picking through:
https://babel.hathitrust.org/cgi/pt?id=chi.087299559&view=1up&seq=10
That will more than get your started. I have more links when ready. The Kippenjungle website will take you a very far distance, but I recommend going through the Scratch Cradle first.
As to your particular situation, your rooster, being White Leghorn, almost certainly has dominant white which will affect all his offspring. A dominant gene displays its traits even when there is only 1 gene present (we, and chickens, have 2 genes at each trait slot).
That means this first generation (F1) you will have yellow down chicks, 100%, both sexes, with some color bleed through depending upon momma. Each of that offspring will carry 1 white dominant gene.
Unfortunately if you keep using that White Leghorn rooster, you will paint yourself into a white corner. Line breeding offspring back to him, you will eventually get more and more White Leghorn look alikes.
If you want to get away from that, you can bring in another rooster (usually very easy to find a nice boy cheap). These offspring from the White Leghorn will only pass that dominant white along 50% of the time. In time, you can breed that out, unless you really like white birds.
Good news is the White Leghorn will pass down excellent egg laying abilities, but a smaller body, so no meat potential.
Good luck with your endeavors.
LofMc
