If you create each weekday as seperate measures and use in a matrix you can field format only the header to red text: This will only work if you use a seperate measures for each day and i don't actually think there is any other way to do it.
In a matrix you would generally have a day dimension as the column. Which would automatically give you the weekdays as columns. This would mean that you can individually field format a column, as all the different says were just part of the day dimension.
But if you have a table, i assume you have measures similar to: