The engine number won't necessarily match the frame number & probably not in your case. The 750-Twin engine was pretty much unchanged thru the entire model run from 1976 to 84, so the base engine number probably wasn't changed.
You can check the frame number (or vin) & engine numbers at CycleChaos dot com or Zedder dot com.
Kawasaki Big Twin models >> KZ750B/G/M/K
The diagrams at Kawasaki dot com & Partzilla have the paint colors, but there are no useable paint codes for matching the paint. PaintWorkz & Colorite are a couple of places that have motorcycle paint. Also, you might be able to find someone on EB who sells matched the paint. Try searching for Sundance Blue paint, then see if that seller has your color. My bike is the sundance blue, so that's how I know about that.
1981 KZ650-CSR. Competition, Sports & Road.