Great Britain 1902-11 Issue 4-D Question

Slowly filling my Stanley Gibbons Sovereign album but several stamps keep me puzzled.
The bi-colored 4d exists in a ordinary paper and a chalky paper variant. This is the first hurdle...

Second one is the determination of the correct colors.
I have 2 4d stamps, I think the brown on both is chocolate brown and I guessed that the left stamp is deep green and the right stamp ordinary green?
Is there an easy way to determine if these stamps are printed on chalky paper?

Any help appreciated!

There are many topics on identifying chalky paper for you to check out on SCF. In short, the front surface is much whiter and smoother on the front vs. the back as if painted, which it essentially is. You might see tiny pits or bubble remnants on the face of Commonwealth chalky papers.

Unfortunately, your right stamp is faded green since that color is fugitive for this era. The left stamp is just "green", I believe.

Older used stamps can be separated by shades, engraved ones tend to be more stable in color and more reliable in keeping their original color. For shades, mint stamps are generally much more reliable as they usually haven't led a relatively harder life.

A chalk surfaced stamp, when rested on the top lip, will feel cool to the touch.

I would call the left stamp deep green, the right one seems a little faded.
Chalk paper is a coating, so look at the stamps with a magnifying glass and see if you notice a coating on the paper.
You can also rub your finger across the top. Chalk paper will feel smooth and slick. Ordinary paper will feel a little rough and not so slick.
Most chalk paper stamps can be identified by using a piece of silver and rubbing it lightly across the top. It will leave a pencil like line on chalk paper. I don't get that reaction much with King Edward VII stamps. They probably used a different coating on them.
When sorting color shades, try to get as many copies as possible. It makes the sorting a lot easier. I put them on both black and then white paper for comparison under my twin spotlamps. It will help you see differences more readily.