ParallelGraph: Convert all colors to tuples.
ParallelGraph: Convert all colors to tuples.

New color generator introduced in 686c2b0 returns np.arrays, which
cannot be used as keys in dict.

Fixes #733.

kwikadi/orange3,qPCR4vir/orange3,kwikadi/orange3,kwikadi/orange3,kwikadi/orange3,qPCR4vir/orange3,kwikadi/orange3,cheral/orange3,cheral/orange3,cheral/orange3,qPCR4vir/orange3,qPCR4vir/orange3,marinkaz/orange3,cheral/orange3,kwikadi/orange3,marinkaz/orange3,marinkaz/orange3,qPCR4vir/orange3,qPCR4vir/orange3,cheral/orange3,marinkaz/orange3,marinkaz/orange3,cheral/orange3,marinkaz/orange3