Function to transition between two colors

gradiate.rb

def gradiate(color1, color2, steps)
  [color1].tap do |colors|
    red, green, blue = (color1 >> 16), ((color1 >> 8) & 0xFF), (color1 & 0xFF)  
    red_diff, green_diff, blue_diff = ((color2 >> 16) - red), (((color2 >> 8) & 0xFF) - green), ((color2 & 0xFF) - blue)

    (steps += 1).times do |i|
      ratio = i.to_f / steps 
      colors << (((red_diff * ratio) + red).to_i << 16 | ((green_diff * ratio) + green).to_i << 8 | ((blue_diff * ratio) + blue).to_i)
    end
    colors << color2
  end
end

gradiate_usage.rb

def gradiate(color1, color2, steps)
  [color1].tap do |colors|
    red, green, blue = (color1 >> 16), ((color1 >> 8) & 0xFF), (color1 & 0xFF)  
    red_diff, green_diff, blue_diff = ((color2 >> 16) - red), (((color2 >> 8) & 0xFF) - green), ((color2 & 0xFF) - blue)

    (steps += 1).times do |i|
      ratio = i.to_f / steps 
      colors << (((red_diff * ratio) + red).to_i << 16 | ((green_diff * ratio) + green).to_i << 8 | ((blue_diff * ratio) + blue).to_i)
    end
    colors << color2
  end
end

File.open('test.html', 'w') do |f|
  f.write('<div>')
  gradiate(0xFFFFFF, 0xFF0000, 10).each do |c| 
    f.write("<span style='background-color:##{c.to_s(16).upcase}'>&nbsp;</span>")
  end
  f.write('</div>')
end