Drawspace lesson Y01: How to draw a Rose on black paper

I decided to skip from section S to section Y. The reason is that sections T and U are about human drawing and shading. Not my thing at the moment.

Section Y, on the other hand, is all about Color drawing so it's going to be fun. 

The subject is a yellow rose on a black paper. It's my first time with dark paper so it's going to be interesting.

This is the sketch I did with my simple, hard colored pencils. The nice thing about them is that you can actually erase it's trace, if necessary. 

This is the drawing with my oil-based pencils.

As it usually happens, I'm happy with the experience, but not with the result.

So here's another try, also on black. (see reference)

After creating a first rough sketch I decided to outline it with white so I could better see the rose on black paper. What a mistake! Should've done it with pink instead. Oh well, next time.

While drawing I began wondering if roses of the same kind have the same number of petals? This is the answer I found online.

Since I wasn't pleased with the result once again I decided to challenge myself a bit more and draw this White Calla. 

This one went really nicely. My only problem here was that I killed my paper pretty fast and didn't reach the richness of the white. 

Any advice here?

P.S. At least now I know what the white pencil is for ;)