Use UDF output in another UDF.

I have a User Defined Function (UDF) called, funnily enough, "SumColoredCells(G3:G336)" which works fine. Because I am adding rows to the spreadsheet, the 336th row will increase, so I wrote another UDF called "LastRow()" to find the last used row. I would like to use LastRow() as part of the range in my SumColoredCells() UDF but if I use SumColoredCells(G3:LastRow()) I get a #VALUE! error. I have tried different things (convert to string, etc) but have not been successful.

This is not a major problem because the spreadsheet is personal and trivial but I am learning to use UDFs just to keep my brain active and challenged. This one is doing my head in.