It seems to me that kadasuki is looking for suggestions for tree that does not lose it's foliage, and a variegated one in particular. It could be a coniferous evergreen or a broadleaf evergreen - terms very common I believe in the horticultural scheme of things to describe whether or not a plant loses it foliage. On the coniferous side there are many that can be recommended as noted in this thread. On the broadleaf side for Zone 6 it becomes somewhat of a challenge. There is a variegated magnolia virginiana - the cultivar name escapes me - and possibly a few variegated ilex. Both will defoliate during extreme minimum zone 6 temps, but should regain growth the following spring. There are some viburnum that are evergreen in zone 6, but these for the most part tend to be large shrubs rather than trees. Sort of a tuffy to recommend a variegated broadleaf evergreen tree for zone 6.

Most jm's do better with morning sun and afternoon, at least, partial shade and if you want at least some color you will need at least 5-6 hours of sun...so it depends on how your tree is situated. Pin oaks are fast growing but IMHO crappy trees ( although ANY 150 year old tree is a treasure!!) I have "inherited" three of them all about 50-75 ft tall. You should be careful planting them too close cause the nasty acorn fall in aug - oct may damage your leaves and small branches of your jm's...fortunatly the acorns are small..( although i've had my head cracked by them more than once and it's NO treat.)Also note the above fast growing statement ...what may be in partial sun this year may become full shade next and trimming ( or in your case falling old dying branches) near your maples may be problematic since pin oak brances are especially twiggy and heavy leading to possible damage of your JM's.( and I don't know how much more growing a 150 year old ree will do).If you have lived with this tree for a while you may be aware of everything I have posted but others here reading this may not!!! All the varieties you mentioned should do well in St. Louis... but the placement may be problematic ...David

@ gardengal-we have had mega-problems with A. rubrum right here in normal, everyday E-Central WI. Our soils run towards the circumneutral and red maple sits and sulks forever here. I don't say these things just for the heck of it, or that other H word for that matter. I know Pennsylvania-like eastern WI-can have lots of limestone outcroppings and near-neutral soils. I wouldn't waste my time-under such conditions-with red maple. If OP happens to not be in such an area (limestone bedrock near the surface), then it might make sense. Freeman maples-including the naturally-derived legacy trees I see all over this area, have no such trouble. Redmaples, on the other hand, are well-established poor accumulators of iron and manganese in soils with a too-high pH, even where those two mineral elements are plentiful in the soil, which is exactly the case here. ETA: But you're right to rarely disagree with me! And yes, I am lol'ing.

I think red leaved trees go best with intensely green plants with interesting foliage to contrast. Red and green are complementary colors in the color wheel. It would work well with cinnamon ferns, Geranium maculatum or bleeding hearts. The green pea like leaves and purple blossoms of Baptista Australis would look good with it but it might be too big.