Question:

When creating a new Expense Estimate record, the picklist value is grayed out in the Expense Type field. The user is not able to select the Expense Type picklist value and create another Expense Estimate record with the same Expense Type.

Answer:

This is the expected behavior. Once there is an Estimate for an Expense Type, that value is grayed out from the picklist.

Related Documentation:

CRM Help Documentation: Budget and Expenses