Fusing motion and color in particle filter
If you can make the assumption that the two observations are independent then the the likelihood function you need is just the product of the two likelihood functions.

If for particle x, the likelihood of it in terms of the colour distribution is p(z_c|x) and the likelihood of it in terms of the motion contour is p(z_m|x) then the likeliood of both observations combined is

 p(z|x)
=p(z_c,z_m|x)
=p(z_m|z_c,x)p(z_c|x)
=p(z_c|z_m,x)p(z_m|x)


With the assumption of independence this becomes:

=p(z_c|x)p(z_m|x)


So just calculate the likelihoods as you have been doing and multiply them.

If you would rather not make this assumption then you need to specify p(z_m|z_c,x) or p(z_c|z_m,x).