Formulas in Symbol defined columns

edited 12/09/19 in Smartsheet Basics

I've defined a column to use RYG.  If I click on a cell in that column I get a drop down to pick from the 3 color ball options.  Now I'm putting a formula in that cell that will do a calculation the picks R, Y or G.  So now all is good; however, If I click on the cell where that formula is and click on the drop down list, it wipes out my formula and it is gone forever.  Any idea how to set up a symbol column that is driven by formula out comes and then prevent people from using the drop down list that comes w/ a symbol defined column?