Also not sure if I understand the question exactly, but I am pretty sure that Conditional Formatting can do the job you want.

If you select the cells with the values in, then select "Formats / Conditional Formatting" from the menu bar, you can put formulas into the conditions windows. So, if you want to find all values that are within, say 0.3 of the mean, your conditions may look something like this, where the ranges are the cells with the values that you want checked:

"Cell Value Is Between =AVERAGE($A$1:$A$8)-0.15 and =AVERAGE($A$1:$A$8)+0.15".

Then press the Format button, select, say, the Patterns tab, select a colour, and all cells in the highlighted range with a value that is within 0.3 of the average will be filled in the selected colour.