I recalled an article from Pontiac Enthusiast magazine (Vol. I No. 2) It also only mentions the yellow and red hoses.

Excerpts from the article, '68-8 Thermostatic Vacuum Switch by Peter Serio

"A manifold connector in the vacuum hose harness to the TVS is used to prevent the hoses from being installed improperly. Note that some of the vacuum hoses in the harness have color-coded stripes running on the supply lines to the TVS. The red-striped hose is manifold vacuum, and the ported vacuum is routed through a small steel pipe forward of the carburetor. The yellow hose (used in 1968 only) is the retard-at-idle-speed vacuum supply."

"There were two different hose harness assemblies used, depending on the year of the car. In 1968 only, with the dual-port vacuum-advance unit attached to the distributor, the idle speed timing is retarded 10 degrees to reduce emissions. After the '68 models, all distributor-advance units were the standard single- hose-connection style. All the 68s use the 5-hose vacuum harness, while the 69 V8's and 71 455 HO make use of the 3-hose type. The two extra hoses on the 68- only harness are the idle-speed retard feature."