Hi Mr Steve,
Not by pressing 'command-C, then selecting all of the sales for one day only'
Command-C placed the currently selected data on the clipboard. If you haven't yet selected any thing,then nothing will be copied to the clipboard.
"I have many Associates that I track Sales and Margin done for each Day of the Week. I enter the data across an entire spreadsheet in Multiple Cells in different areas on the Spreadsheet. "
If that's true, you'll have a difficult time collecting the data for a specific weekday. If your data is better organized than your description implies, what you want can be done relatively easily.
Here's an example using the least complex arrangment of only the data required for the highlighting to occur.
Column A of Data are entered values—the names of the sales associates. Column B on this table also contains entered date, but for your 'real life' case, these would be calculated from the individual sales on the day being tracked.
Columns A and B of Calculations contain the formulas below, entered in A2 and B2 as noted, and filled down as described below the formulas:
A2: RANK(Data::B,Data::B,largest-is-high)
This calculates the rank of each associate's sales figure within the list of all figures in that column.
B2: =LOOKUP(ROW()−1,A,Data::A)
Filled down to row 4. Cell Fill colours entered from Cell Format panel.
The three copies lookup the name in Data, column A associated with each of the top three ranks (1, 2, 3) in column A of Calculations, and copy that name into the cell containing the formula.
Conditional Highlighting:
Cells in Data::column A have the conditional highliting rules shown below:

CONCEPT ONLY for the moment. The highlighting will fail when two or more of the top three scores are duplicates. Easily corrected, but I'll wait for more details on th structure of your data before adding that to the mix.
Regards,
Barry