Lack of color displaying composite video
It  would appear that you have significant ground current noise between the two systems or some other large CM noise.

The VDP scale is 1/4 of the DVD yellow scale to see that same size sync tip and chroma burst. The amplitude must be double amplitude for a 75Ohm source and load and the same as the DVD player.

The output level for chroma sync if too low or noisy would disable chroma video from being displayed in the VDT.

The VDT shows a LOT of pixel clock noise on the display.  

Shields up and improve grounds.