Green clubs and blue diamonds
There are already some games that use this type of deck; such as Tichu. A Tichu deck contains 4 suits in 4 different colors (although they are not the same traditional 4 suits).

For most games out there; this idea would make the games slightly easier to play; because it would be easier to distinguish a Spade from a Club, and a Heart from a Diamond. Most traditional trick-taking or melding games would benefit from this.

However, there are a few games where not only suit, but color, also matters:

Canasta - Red 3s have separate rules from black 3s. It doesn't matter whether a 3 is a Spade or a Club, but it does matter if it's black. To play Canasta with your custom deck; you would have to remember that both a Club and a Spade have one rule, while a Heart and a Diamond have another rule.

Klondike Solitaire - Red cards can be moved onto black cards and vice-versa. So again, this would be more difficulty to play with your custom deck; as you would have to look for cards of 2 different specific suits rather than just look for cards of a specific color.