Since you don't say what zone you're in, it may be difficult to
recommend trees for you. But, if you are in the right zones,
decorative plums are nice with their deep burgundy leaves which would
be a lovely contrast to the green from your surrounding forest.
Japanese maples are a great choice because many can give you three
colors for the three seasons. You can get them with either green or
red summer foliage, and the autumn colors can be either red or
brilliant oranges and yellows. Some start with one color green, like a
light, lime or yellow green in the spring and go to another darker
color green in summer. You can research them at many sites. Just
google Japanese maples and you'll find a lot of site with pictures and
explanations.
Dogwoods come in white, pink and red flowers; but the flowers only
last a small time in early spring. Then the leaves go green. If
you're in the right zone, you can get flowering shrubs that are like
small trees and they can come in various shades of white and pink.
There are a lot of beautiful flowering spring trees like flowering
cherry, styrax japonica which is a 20-30' tall, narrowish tree with
charming white or pink, hanging bell shaped flowers in the spring.
Your location and the size of tree you want is your first
consideration. You can check out many of the on line nurseries for
pictures and more detailed information on what would work for your
area.

Regards,
June