Is the trim and wall using same latex paint?
A common approach is to use flat paint on walls and satin or semigloss on trim. This is independent of whether the paints are latex or oil based. 

Even if the same color, a higher gloss paint tends to look lighter than its flat mate.

Often an additive is included in trim paint to make it lay smoother and to reduce brush marks. Again, this is done on both water based and oil based paints.

It is uncommon to us the same paint on walls and trim. Flat (or other low luster textures) are less durable and do not hold up to the touches and bumps that trim receives. 

Some purists use latex on walls and oil based finishes on trim. There are now water based alkyds that are positioned somewhat in between water and oil.

When repainting, the key is to clean, sand, and prime (if needed), and then put quality paint of whatever type on top. More and more, even pros are leaning toward high quality water based paints. Plus you avoid that whole nasty VOC stuff.