Find the closest colour block for each pixel

[LiamS47]

I am using Excel to help me create art in Minecraft with my children. I've worked out the RGB values of each block in the game and the values of each pixel in the picture I want to create. To begin with I'm unsure whether I should have each of the RGB values in separate cells or in one cell? (i.e. Row A is all R values, Row B is all G values and Row C is all B values OR Should it be set out as 128,91,100 for the R,G,B values) Secondly, once that has been decided on, I need to know how to find the closest colour block for each pixel (i.e. the pixel may be 100,100,100 and the blocks may consist of these three:block1 is 100,99,101, block2 is 30,27,237 and block3 is 250,90,8 … I want it to change the pixel values in the cell 100,100,100 to say block1 as that is the closest). Any help would be great. Thankyou