Betta Fish: I love how the colors change!

So for context I was looking for an alien for like 3 weeks and had a tank setup for him but could never find an alien. Then I went to Petco to get some food and finally found him. He was pitch black and was just constantly laying on the ground no swimming at all, and seemed pretty skinny to me. Got him and brought him home acclimated him and all that good stuff and fed him which he actually started eating pretty much right after I put food in. The food can be seen in the first image which are the white spots. But like after 4-5 hours his colors changed to what is in the second image. Also sorry if I talked too much it’s just that I’m really into betta fish right now. Also if you’re still reading this does he look skinny at all to you guys.