In 1974 it could be quite colorful. Nationwide, many cars had already been repainted for Amtrak, but the Northwest trains were running full, due to Spokane's Expo '74. After the oil shortage of 1973, Amtrak had leased a number of BN cars, so the EB and NCH still had a good mix of Amtrak, BN, GN, NP and CB&Q cars that summer.
Also, while the usual power was the SDP40F, F units were still being used. Amtrak had 11 of their own for the Chicago-Seattle routes, but also leased almost 30 from BN, so the power could be colorful as well. Before the SDP40Fs took over, solid Amtrak consists were very rare on the Empire Builder.
The summer of 1974 was the only time I ever saw a "second section" of a scheduled train. The eastbound EB arrived in Pasco, with its SDPs, and green class lights lit, and 15 or 16 cars. A few minutes later, the second section appeared, with four Fs, and another 10 or 12 cars. I didn't think to write down what was in the trains, and it was too dark for pictures. The second section was entirely Seattle-Spokane passengers, going to Expo, and terminated in Spokane.
Usually the extra traffic used the temporary "Expo '74", through Wenatchee, so I don't why the second section.