Conditional formatting in Workfront reports is more limited than in an Excel sheet - the syntax when using a custom expression is not well-documented, and there isn't a way to do conditional formatting based on the value of a cell. Instead, you have to put an expression in the conditional formatting code that would equate to the same result as the cell value, which doesn't work if the value of the cell is determined based on a collection of tasks in a project report, for instance. Allowing formatting to be based on the value contained within the cell would make it easier to apply conditional formatting if the cell is calculated using a custom expression, and possible to apply conditional formatting to collections.