you won't like it...change your text color in your report. as far as I know, you have basically no control over the export from CR to anything else. Which means, if there is a glitch in CR exporting the cell backColor, you're out of luck.
You might try exporting to PDF. If it exports there OK, maybe you can use that to convince your client that the data is there. If they don't want to go to the next step to change the color (of the cell or the text), then you probably need to change the colors of your report.
HTH