Congrats on your loss so far! That's great that you've stuck with it. I also had very little weight loss in week 3 and part of 4, but now I've gone back to losing about 1/2 pound per day.

The keto sticks measure body fat burned as well as fat consumed that is burned. There is no way to distinguish between the two. You might have gotten dark purple BECAUSE you had a high-fat meal. All the sticks tell you is that you're burning fat, they don't distinguish between the two kinds.