Need to compare two columns in separate sheets, highlighting differences on each sheet

[MoBecca]

I've searched high and low and cannot find the precise macro needed. To make it as straight forward as possible:
I need to compare "Sheet1" column "Serial Number" with "Sheet 2" column "Serial Number"
If any serial numbers are found on both sheets, they should remain unchanged.
If any serial numbers on Sheet1 are not on Sheet2, I'd like each to be highlighted RED.
If any serial numbers on Sheet2 are not on Sheet1, I'd like them highlighted YELLOW.

As a side note, I should explain that the column headings "Serial Number" are listed in row A of each sheet.

I plan to just copy/paste my data into Sheets 1 & 2, to make this easier. It would be amazing if could find a way to compare the two original sheets, but I fear it's impossibly complicated due to an inability to name the columns, and how they vary from sheet to sheet. I would need a pop-up prompt to designate the row range/column to be compared in each sheet, since it would change routinely.

Thanks in advance for any assistance or even pointing me in the right direction. I LOVE this forum!

 

[Special-K99]

Use Conditional Formatting

on Sheet1!A1
=ISNA(MATCH(A1,Sheet2!A1:A100,0))
format as Red
Use format painter to copy down the column

on Sheet2!A1
=ISNA(MATCH(A1,Sheet1!A1:A100,0))
format as Yellow
Use format painter to copy down the column

 

[MoBecca]

Thank you SO very much for your help! I must be applying it incorrectly, however, because nothing happens.
On Sheet1, I highlighted the first cell in the Serial number column and clicked Conditional Formatting/New Rule.
I highlighted "use a formula to determine which cells to format"
I pasted the following: "on Sheet1!A1=ISNA(MATCH(A1,Sheet2!A1:A100,0))" and clicked "format" choosing red fill and clicked OK.
I then highlighted the cell to which it was applied, clicked "format painter" and dragged the highlight to include the whole column (down 500 rows).
I repeated these steps on Sheet2, using the second rule "on Sheet2!A1=ISNA(MATCH(A1,Sheet1!A1:A100,0))" again using format painter.
Nothing changed at all, despite there being many cells that should have been filled on both sheets...