Acid colour-changing trick?

i recently saw this trick, in which a man had a jug full of clear acid, i don't know what acid it was, but he had 5 gles, all with indicators inside them, he poured the liquid into the 5 gles; one went pink, the other blue, yellow, black & the last one white. he then poured the gles back into the jug and the colours changed again, and when he finally poured in the clear liquid from the last gl, the acid in the jug turned clear ! What acid is this, and how does it work?