Grulla/Grullo?

So this is kind of a silly question (well, two)... But I honestly don't know! What's the difference between Grulla and Grullo? I know they're both identical colors, but some people say it's just a spelling preference, and others say Grulla is feminine and Grullo is masculine. Also, pronunciation of the two? I speak French, not Spanish, and I'm pretty sure they're Spanish words... I've always said "Grew-la" ("grew-low") but I think they might be pronounced differently because they're Spanish terms?

Both the words mean the same thing, spanish speaking people say that a/o means masculine/feminine, either way no matter how you say it people know what you talking about. As for pronouncing it i've herd Grew-la and Grew-ya

Like lilkitty said: It's a gender thing. It's meant to be Grulla = female. Grullo = male. And it's pronounced Grew-ya and grew-yo.

Fun fact:

The color is named after these guys.

Im from the uk and as far as I've heard, everyone over here pronounces it like Gruh-lah or gruh-loh... not that its a common colour over here. But theres a couple of grullas/grullos in a dealers field near me. Poor things have just been left in the muddy field all winter only getting a bail of hay between about 20 - 30 horses every now and then. A few of them have rugs on but theyre ripped and hanging off, im pretty sure some of them are stallions & most are mares & clearly some are in foal. A few have real bad rain rot & they all look so depressed. If I could afford it, id buy them all & give them better homes </3

Thanks everyone for clearing that up for me :)
KC- That's terrible! There was a couple horses at this barn right near a place I used to board at that sounds similar. They only had 4 or 5 horses, but they were all in a paddock that was probably about half an acre and they were skin and bones. People used to throw hay in for them when they knew the owners weren't around because the horses were so hungry they were eating the bark off the trees.... It amazes me how cruel some people can be.