In a quick test, I was able to accomplish what it sounds like you are wanting with the following.
- Using CTRL + Left Mouse Click, Highlight one rows worth of cells that you want included in the validation; F, J, and N in your example.
- Go to the Format menu and choose Conditional Formatting
- In the Conditional format rules pane, change the "Format cells if..." dropdown to "Custom formula is"
- In the formula field, put:
=($A1:$E1)=max($A1:$A1,$C1:$C1,$E1:$E1)
where A and E columns would be your extreme left and right columns (F & N in your example). Don't worry about the columns between because you aren't applying the rule to those other fields, and also aren't including them in your MAX() calculation
- Change the "Apply to range" as far down your columns as you require (screenshot below)
- Style as you see fit and click Done
On this last screenshot, I'm showing that I went ahead and made my column range huge, but as soon as I filled in data on row 22, it picked up the max value from columns A, C, E, and formatted those columns accordingly.