how to diversify colors with close saturation and brightness when converting them into grey scale?

Hi, I am trying to increase the quality of color segmentation, which I find most Matlab tutorials convert the image into greyscale at the very beginning. While there could be problem when two colors(for example, red and green) have a close degree of saturation and brightness, and after conversion they almost mix together, which will totally ruin the final effect if these kind of colors are adjacent to each other. Is there any function or tutorial of how to separate color after the conversion? Thank you!