Nice start on these. You are headed in the right direction. When you get your shapes worked out well, pay very close attention to the values. You want to match the values you see as closely as you can. It is important to be very honest about what you are seeing. try to put the accurate value down with each stroke as otherwise you end up having to fix things along the way and being accurate will save you time. Really take the time to observe and compare and choose the right value. If you are off, adjust it, don't keep working and come back to it. You are doing great...just need to focus in on value a little more.
Keep it up.