changes made:

added sources as triangles of laser
added ? slider with color indicated with reference made to Jose Ignacio Fernández Palop vcolor http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=1037.0
reorder blue green red in ascending order of magnitude
set default as double slit
made a, d, D and y
made intensity selectable
redesign the layout to suit left to right with right panel showing the screen
laser redrawn
slits added
text of views added
added point yp with reference made to tat leong yp http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=2778.0

enjoy!