If they are still light at 4 weeks, they are probably going to stay that way. You may end up with both white and gray, but if spots were going to show, they probably would have already.
I had a large batch of fry born of a White Mickey Mouse Platy and a Blue Mickey Mouse Platy. They are ALL White (or grey or light blue, can't tell yet) with Dalmation spots on their entire bodies
Where all the spots came from, I have no clue, but they are adorable
But the spots showed up in about 2 weeks. They have gotten more spots over time, but I already knew they were spotted by then.
I also had a Pineapple Swordtail that was my Mama Sword. She gave me some of the prettiest babies, but they were all different colors. From one release I got 4 different colors......almost yellow with a little light orange, Pineapple with light orange and yellow, Pineapple with dark orange and yellow, and solid dark orange.
I'm sure your not all that interested in all the fry I have had, but I wanted to give you an idea of what can happen with livebearer colors.
Good luck with the little ones and post some pictures if you can. I would love to see them