How to classify the color of each pixel using its RGB values

Hello. I'm trying to classify the color of each pixel using RGB values as red, yellow or blue. But the problem I have is that my classification for REDPIXEL includes colors: pure red/pink/reddish/red-orange and all those colors that look red or around that area to the human eye. SO, the range of the variance of RGB values is enormous. I've tried to classify using an approximate range for the color, but I'm sure I'm leaving out pixels & there must be a better way of doing this. My code is as follows:

img=imread('1.jpg'); %Reading the image I want to work on

RedPIXELS='1010-808kPa';%The classifications YellowPIXELS='700-600kPa'; BluePIXEL='270-0kPa';

img=imread('1.jpg');

for k=1:vidHeight-1 if img(k,k,1)>250 && img(k,k,1)-img(k,k,2)>100 && img(k,k,1)-img(k,k,3)>100

img(k,k)=RedPIXELS; if img(k,k,2)-img(k,k,1)<50 && img(k,k,3)<10 img(k,k)=YellowPIXELS; end

    end 
end

[Star Strider]

Unformatted duplicate of: http://www.mathworks.com/matlabcentral/answers/264060-how-to-clasify-the-color-of-each-specific-pixel-to-some-constant