List of viewed Discrepancys :
Color Selector : I use the "color picker tool" and I can access the "tool options" and then select the desired options, such as select from choosen layer. But when I am using the "free hand brush tool" and press "Ctrl" for the "color selector" I cannot use the options I used on the "color selector" nor access the "tool options" to change them on the current state.
Blend Mode : I tryed to mix a "color" layer and a "greyscale" layer to get a perfect mix of values, considering the reference color values that I established with regular increments of lightness. For this I transformed my aimed color to have 50% luminosity and painted on a layer with a blending mode of "Overlay" and then placed it over the greyscale layer. This set up made the colors mix and get the desired mix. However I noticed that the same operation in Gimp and in Photoshop would have to be done with blend mode "hard light" instead of "overlay".

Why am I trying to make these Mixs :
I was trying to make a painting workflow in which I could have "color" in one layer and the "greyscale" in another layer and if possible paint them together too.

Why I think this matters :
Color Picker : I want to see a rendered color but pick a color from a selected layer and this without having to change tools when I can use the ctrl toggle.
Blend Mode : I think the names kindda represent the math operations that happen with colors and there seems to be a common standard more or less precise depending on each program. But this makes me think something is just swaped.

Images to ilustrate :
Color Selector : http://www.pasteall.org/pic/show.php?id=97988
Bland Mode : http://www.pasteall.org/pic/show.php?id=97987

Whacky Ideas :
1) Fliter layer that could set all pixels with the desired luminosity. this would be good to be set by default in 50%. Would reduce the amount of layers and groups. This could do what I am doing with the extra group layer (blend=Overlay) in which I am composing the natural colors inside to be normalized with a 50% grey layer (blend=Lightness) so it can mix correctly with the greyscale below.
2) Layer Operation in which you could split the color information ready to be mixed. One layer you would have the Hue and Saturation=50% (Normalized Colors) and the other layer would have the Lightness (greyscale). This would make the merge and split a good workflow to use as you could easily separate and join again when needed.

Notes :
With all these operations on the dog picture I managed to mix all colors back and have a delta of 10 points max in saturation considering the original picture. I would love to be able and reduce this if possible, if there is info on how to make these operations correctley I would love know and read if possible.

My Thanks in readding this