Apple tree fire screen - half the stems filled in

I've got half of the stems filled in in Madeira stranded cotton 2213, and I have to say it's not looking like I'd wanted it to.

Here's the loop at the top:

Hmmm... it's not right, is it.

Giving it the benefit of the doubt, I carried on:

No, definitely not right.  The palest shade looks too pale, far paler than it does in the packet, and the transitional shading between it and the darkest one is hardly noticeable at all.

Something is going to have to be done about this, but I don't want to start any remedial work on half of it, as it could end up looking unbalanced: better to complete the stems, and then sort them all out in one go, when I can see how the full piece is working.

Or that's the plan, anyway.  We'll see how it goes.