Beautiful assignment.
Both images are very strong both from an artistic and technical standpoint. Let’s start by discussing the first image (blue and white). The image is strong in its color qualities because you’ve limited your color palette to blue, white and black. Your horizon line is well placed, your objects are well composed and the photograph has a slightly informal balance to it which gives it a more interesting and dramatic look then if you choose to compose the shot with more symmetry.
Because you’ve placed the sun slightly off center and included more weight of the tree on the left than you did on the right, it gives the image a more interesting look in my opinion.
Your second image is also very strong. The yellow and green combination is one of my favourites, so I’m slightly biased, but like the soft feel of both colors.
I just want to make you aware of a few things regarding this issue. First of all, I just wanted you to be aware of the amputation of the flower petal on the right side of the frame. I think I would have preferred to see the entire flower in the frame. Although I must say, for a small amputation (which I usually find very distracting), this one doesn’t bother me that much.
The other issue I wanted to point out is the grain in the photograph. It’s not wrong what you’ve done but I wanted you to know that it may be an issue of ISO speed. If you shot with too high of an ISO speed you’ll have digital grain in your photograph. Using lower ISO speeds gives you crisper images, which is very important to know if you’re going to be blowing up images.
When your image is small, it looks fine. But when I look at your image at full size the “grain” looks like a noticeable colour “noise”. Look closely at the pixilation in the enlarged version and notice the random colors of pixilation. That’s generally not desirable.
Other than that…. Beautiful photographs! Well done.