Excel e-mailing sheet missing cell colors

[Sypher2]

I have a spreadsheet that I e-mail daily to internal staff. It has a lot of conditional formatting which change the cell background colors. All the colors and formatting have e-mailed fine.

This month, I started a new spreadsheet. All coloring looks fine in the workbook, but e-mailing the sheet has many of the cells just plain white.

Any idea what's going on?