Excel 2003
I need a column formula that recognizes to change a cell reference when
there is a blank in the row. For example - current data:

column a column b
row 1 RED
row 2 12345678
row 3 87654321
row 4
row 5 BLUE
row 6 93748504
row 7 87323956

Needed data:
column a column b
row 1 RED
row 2 12345678 RED
row 3 87654321 RED
row 4
row 5 BLUE
row 6 93748504 BLUE
row 7 87323956 BLUE