Combobox logic

Question

I have Combobox A, and Combobox B. Both combox A and B are related to each other.

Combobox A : Color serial No

Combobox B : Color part No

Note:  Color serial No, and Color part No belongs to a color type.

if user select an item in combo box A, combo box B will populate exists Color part No that are related to Color serial No. from the dataset or database.

or

if user select an item in combo box B combo box A will populate exists Color serial No that are related to Color part No.
from the dataset or database.

I am basically limiting the user to only query the items that only exist relate to each other by color serial and part no.

Can someone give me an ideal to effectively design this logic. At the moment.