jim,
In looking at my 68 Data book, std bucket seats were available in the Eldorado in black (451-B) and sandelwood(482-B). Not surprisingly, this was also true for the Deville Convertible.
In looking at the special order section, you could get two-tone combinations. All fabric options, leather colors and body style (except Calais or 75, buckets not available) required a special order.
So Jim, If they made it, you could get it in the Eldorado that year!
For Emporer Blue, the data book says that though April 67 the percentage of use was as follows: (2 most popular colors follow)
Deville Convert 3.0percent (white, san mateo red)
Eldo 3.8percent (white, baroque gold)
60S,Brghm 6.2percent (black, baroque gold)
G/N/J/B/L 2.5percent (white, baroque gold)