A "yellow" spark is normal unless you're running metal-core plug wires. The "it needs a hot blue spark" advice is at least 50 years out of date, but some of the people who give that advice have no idea why they're saying it, they're just repeating an "old mechanic's tale" they learned from some oldtimer who didn't know what he was talking about, either. Any radio-frequency suppression wire will change the color of the spark, and make the carbon contact button in the center of the distributor cap last three times as long in the process.
Are you doing the suggested hydraulic lifter adjustment that's in the service manual? Try using half as much preload on the lifter after the slack is taken out of the linkage. Some manuals recommend as much as 1 1/2 turns of lifter preload- - - -I believe that's way too much.
Jerry
