[Gimp-user] Help with color of several shades

[SArtino <forums gimpusers com>]

Hi everyone.   I'm not new to Gimp, but I'm also not an advanced user of it. 
Recently we've started a portfolio of our product at work (we make block/bricks)
and needed a way to display our product.  I suggested a small wall platform and
we could stack the bricks on the platform making a small wall and take a picture
with wood in between as the mortar joint.  So, since these are designer bricks,
the mortar joints between range in shades from almost black to white, and colors
from dark brown to red to a buff (almost yellow).   So, since we make about 20
different color brick blends, and there is probably an equal amount of mortar
colors the contractors use, I suggested painting the wood edges to a bright
green because we make no blend that contains green, sowe can use a single photo
of one brick wall, and change the color of the green mortar joint to whatever.  
1 photo of each wall blend, edit 20 different mortar colors. Sounds like a
simple idea right?

It there anyway to change the shade of one color spectrum to another without
having to zoom in and painstakingly draw over it?  Meaning all instances of said
green (shadowed and gradients) to another color without effecting the rest of
the image in gimp?

Attachments:
* http://www.gimpusers.com/system/attachments/242/original/IMG_20160413_133407.jpg

-- 
SArtino (via www.gimpusers.com/forums)