required fields in a table

Enclosed is a table which is protected, except for columns D,F,G.
I want the user to be able to fill out data only on the above mentioned columns, therefore I will protect the sheet except for the three columns.

My question is, is it possible that if the user puts a number in the QTY column, then he can not continue to the next line, unless he puts something in the Color cell. The data in the color cell can be anything he wants (I am sure that in that cell he will put the color), but it is important that once something was put in the QTY cell, the next cell must be the Color cell and the user will be stuck there as long as there is no data in that cell.

Thank you
Raphael