How to grey out the cost amount column while creating a budget for only Billable task and vice versa

While creating a budget with Financial Planning Amount "Cost and revenue in same plan version" at financila plan type. Ask is when we are creating a budget for only chargeable task then Revenue amount column shall grey out and when creating a budget for only billable task then Raw cost amount column shall grey out. That is the user shall not be allowed to fill in the amount.