Anybody feel free to correct me or add opinions.
I'm going to just list some off Townline Hatchery's page, though for a very dark egg layer, you can't beat the Marans (not offered by Townline). Townline's selections tend to handle cold weather just fine. My girls lay through the winter... the newbies always laid better than the year olds or two year olds.
The Brahma hens are about the calmest I have. They're quiet, but like to chat and tell me stories when I come out to the coop. I think it's funny.
My Australorps (though I think 1 is actually a Jersey Giant) lay an almost pinkish colored egg (another shade of brown really), and have been good broody's.
For the blue/green eggs, get your basic Easter Egger (Townline calls them the Ameraucana Strain).
I've had both the Silver laced & Golden Laced Wyandottes... They seem to have a lighter brown, almost peach/tan colored egg that looks nice in a multiple color egg basket.
My Barred Rock hens, during their first year, seem to have a relatively dark brown egg, though they do lighten with age. Our current Barred Rock seems to take "the egg song" to the extreme. She's very proud of the eggs. She serenades each lady on the nest box & must announce when EVERYBODY lays an egg, and for herself... she likes to give a prelude as well. She's an "egg song" instigator and tends to raise the egg excitement with the other chickens. LOL. It's quite funny actually.
For production, it's hard to beat the California Grey Leghorn. They lay often, the white eggs look just as beautiful in a carton next to multiple other colors (especially in contrast to the Marans dark browns), and their feed to egg ratio is the best.
Also good for production are the Rhode Island Reds, New Hampshires, ISA Browns, and Amber Link. They'll all lay consistently with relatively similar brown shades.
I've never had the Orpingtons (I'm not sure why, I've always wanted to), or the black sex links. I think they were on my list to try this year, but the "chicken math" had the coop full before I could. LOL. Maybe next year.
If your MIL wants a colorful egg basket with only 4-5 cold hardy hens, and easy/cheap to get by going to Townline... She should pick the California Grey (White) Leghorn, Easter Egger, Australorp, Wyandotte, Any 1 of the regular brown egg layer (RIR, NH, ISA, AL, BSL), and if you can convince her of 6... find her a Marans. This would make a good starter flock. Although this is just my 2 cents & probably not even worth that much. There are a TON of correct answers here.