What you have is, oh I have no idea. The funny thing is it looks like a digital artifact.
I'm going to take a stab at this. You are going from your Laserdisc player to the Canopus ADVC-300 into your Mac?
I see that the ADVC has a lot of image cleaning and stabilization features. Have (can?) you play with them?
The problem looks very similar to what you can see in Cowclops' version 1 SW release.
He captured the video to digital tape and then into a PC.
Along the way, the color space changed. The digital cam utilizes 4:2:0 and DVD is in 4:1:1. The result is the worst demoniator of 4:1:0 which causes banding in solid red and solid blue colors, a lot like what you're showing.
I don't know if that's what your ADVC is doing (I'd hope not), but I'm just saying that's what it LOOKS like.