Colour is the first thing you notice and the least reliable thing to rely on, because light, moisture, lichens and age all change it.
Bark colour
Pale and white
White or very pale bark stands out in winter. Paper birch is chalky white. Quaking aspen is pale greenish-white with dark scars. American sycamore has creamy white patches high on the trunk and branches. American beech is pale grey and smooth.
Dark and black
Black walnut is dark brown to black, and so is black cherry. Wet bark looks darker than dry bark, so compare trees under the same conditions.
Red and orange-brown
Red pine has broad reddish-brown plates. Scots pine has bright orange-red upper bark, especially against blue sky. Ponderosa pine develops orange plates as it ages. Eastern redcedar and the cypress-family trees tend to be reddish brown and stringy. Paper birch is sometimes reddish when young, and river birch is salmon to cinnamon.
Green tints
Algae and moss on the shady side of a trunk turn bark green. That is a sign of moisture and not of species. Young aspen bark can look greenish from the living layer just beneath the surface.
Why colour misleads
Lichens colour bark grey-green, crusty white or yellow. Sunlight bleaches it and rain darkens it. Colour also shifts with age: the young smooth bark of many trees is greyer and paler than the furrowed bark of the same tree later. Use colour to start a search, and confirm with texture, leaves, buds and fruit.
Twigs have their own colour
The twigs of a tree are often a different colour from its trunk, and the colour is steady enough to use in winter. Red maple has red twigs and buds. Dogwood twigs are often purplish. Birch twigs are slender and reddish brown. Compare twig colour with the bark of the same tree before you decide.