Calculate a Gradient

gradient_calc.rb

gradient_percentage = 0.10

# Split into RGB
red   = backgroundcolor[0,2].hex
green = backgroundcolor[2,2].hex
blue  = backgroundcolor[4,2].hex

# Add percentage (could subtract if you want to darker)
red   += (red   * gradient_percentage).to_i
green += (green * gradient_percentage).to_i
blue  += (blue  * gradient_percentage).to_i

# Convert to base 16 string and pad with extra 0 if needed
red   = red.to_s(16)
green = green.to_s(16)
blue  = blue.to_s(16)

# Pad with extra 0 if necessary
red   = ('0' + red)   if red.size   == 1
green = ('0' + green) if green.size == 1
blue  = ('0' + blue)  if blue.size  == 1 

# Make sure numbers haven't overflown
red   = "00"  if red.hex < 0
red   = "ff"  if red.hex > 255
green = "00"  if green.hex < 0
green = "ff"  if green.hex > 255
blue  = "00"  if blue.hex < 0
blue  = "ff"  if blue.hex > 255

gradient = red + green + blue