Konnichiwa!

Below is a list of all of the RGB hexcodes that correspond to the in-game colors used for all 18 different types of Pokémon.

It is worth noting that I got these hexcodes by looking at the code of pages on Poképaste, which uses these same hexcodes for various things such as Pokémon, moves, and Z-Crystals to denote their type.

[Spoiler=Pokémon Type Hexcodes]Normal (168, 168, 120)
Fire (240, 128, 48)
Water (104, 144, 240)
Electric (248, 208, 48)
Grass (120, 200, 80)
Ice (152, 216, 216)
Fighting (192, 48, 40)
Poison (160, 64, 160)
Ground (224, 192, 104)
Flying (168, 144, 240)
Psychic (248, 88, 136)
Bug (168, 184, 32)
Rock (184, 160, 56)
Ghost (112, 88, 152)
Dragon (112, 56, 248)
Dark (112, 88, 72)
Steel (184, 184, 208)
Fairy (238, 153, 172)[/Spoiler]

It is also worth noting that the colors used for stats on Poképaste are (mostly) the same as those used for types, and are as follows:

[Spoiler=Pokémon Stat Hexcodes (Poképaste)]HP (255, 0, 0)
Attack (240, 128, 48)
Defense (248, 208, 48)
Sp. Attack (104, 144, 240)
Sp. Defense (120, 200, 80)
Speed (248, 88, 136)[/Spoiler]

Of course, the particular colors that they assigned to these particular stats are a bit odd IMO, and so for things that I post here on Paint (like the movesets posted on this group page of mine in a group of DC's) I use these colors instead, which match the colors assigned to each stat in the Pokémon Super Training screen in the Gen 6 games, as well as the stats screen in the Gen 7 games:

[Spoiler=Pokémon Stat Hexcodes (Draconid_Jo)]HP (120, 200, 80)
Attack (248, 208, 48)
Defense (240, 128, 48)
Sp. Attack (152, 216, 216)
Sp. Defense (104, 144, 240)
Speed (112, 56, 248)[/Spoiler]