Refraction and reflection

Playing with faceted glass tonight. This glass souvenir of Sydney Opera House is made of clear glass with just a green baize base and has an etching of the opera house on the top surface. I stood it on a plain white base with no direct light source and no obvious colour near but there was a myriad of reflected colours when viewed from above.
In the old days I used to use Cokin filters and prisms which produced similar effects - but that was with a film camera - and too expensive to just play with as you couldn't see the result until the film was processed. Digital is much more fun! ( I wonder if the filters would work on the DSLR - I still have them ? )