In Young's double-slit experiment, the source is white light. One of the holes is covered by a red filter and another by a blue filter. In this case,
 

The figure shows a standard two-slit arrangement with slits ${\mathrm{S}}_1, {\mathrm{S}}_2. {\mathrm{P}}_1, {\mathrm{P}}_2$ are the two minima points on either side of P as shown in the figure.

At ${\mathrm{P}}_2$ on the screen, there is a hole and behind ${\mathrm{P}}_2$ is a second 2-slit arrangement with slits ${\mathrm{S}}_3, {\mathrm{S}}_4$ and a second screen behind them.