I assume you have a range of cells that you want to have this happen to. Say the range is B4:J10, select that range, then go to Format > Conditional Format, and on the left, in the dropdown box, make sure it is "Cell value is", then in the middle dropdown choose "is greater than", then in the right box, type 99. Click the Format button on the middle right and set your font color. Click OK.
While still in the Confitional Formatting dialog box, click on the Add button at the bottom, and choose same as above, only in the middle box, select "is less than", then click Format button and set your font color. Click OK. Click OK.
old, slow, and confused
but at least I'm inconsistent!