There is a way to tell gender but I'm not very good at it. To get my dark purple footed mystery snails to mate I just threw all 7 of them into the same 10 gallon for 2 months and finally have eggs, pretty sure I had all females in there until 2 weeks ago when I found one that I had forgotten I had put into the bedroom. I had signifacantly less dark colored ones than light colored ones so really wanted these to breed.
If you want babies (or alot more snails) then if they do successfully breed then she will need about an inch above the water line that is clear of water so she can crawl up there and lay the eggs, if it's to full she may just crawl around and find a way out of the tank. An inch works for me because it forces her to stop and move, leaving smaller clutches up there to regulate how many snails hatch a bit. I let 3 small (less than 3/4 of an inch big) clutches hatch and have well over 100 baby mystery snails that are smaller than a pea at the moment. After you get the number you want, just scrape the eggs off the aquarium and throw them away if you don't want them to hatch, and then keep an eye every week up there so you can remove any eggs that might pop up if you don't want hundreds of surprise mystery snails. I almost missed a huge clutch in my 29 gallon but found it in time, 3 more days and I would have had hundreds more snails to deal with. I'm going to start culling colors soon, to get them a managable number to be able to grow a bit and sell with my plants. Probably going to give half of them away to people that want them.
Colorwise, you'd probably get some blue, some yellow and maybe some blue/yellow striped - plus if they came from a mix of color somewhere down the line you could have another off color thrown in also. Half of my light footed purple snails look to be a beautiful ivory right now but as I found out with the last batch, as they get bigger the purple color could develop later with time.