I've been working with yellow mostly for today's session (while watching old 50's Westerns, which I love).
The close-up shows the amazing difference just the stitches make while using the same thread. The sunflower petals and the little square things on the diaper pattern are both DMC cotton floss #3821.
The difference is that I also used Kreinik Blending Filament #028 on the sunflower. The squares in the pattern are simply floss in Scotch stitch - and they look lighter and brighter than the basketweave of the flower petals, as they lie flat and reflect more light.
I decided the flower centers in the blue ones needed to be lighter and without sparkle, so used DMC Satin floss there with no blending filament. The photo of the threads shows the versatility of this BF, as you can see that the yellow is dark, and blends beautifully with the floss. There is also a light BF, which I've enjoyed using with the next shade lighter in the floss on other things.
The green (Kreinik BF #009) looks rather dark to blend with #987 green, and I was afraid it wouldn't work for this - but it blends very very well, and exhibits a light, bright random sparkle which livens it up a lot. This shows that one needs to experiment, even if it doesn't look quite right lying on the table!!
The next photo shows the #018 Kreinik metallic - two are blending filament, and two are #12 braid. The one on the far left is just plain 018. ( I didn't have BF to show) The dark navy on the fat spool next to it is HL, and the small spool to the right of that is blending filament HL. The light one is Vintage BF. The floss is #336. (the background on this piece.) The Vintage BF is what I used with the navy floss on the square "bump" stitches in the diaper pattern.
The arrow in the close-up picture is pointing to the only one I could get the light to hit correctly to show one little sparkle. In person, it's an interesting effect, and it looks much better than it would with the darker HL version.