Every Pokémon has a Nature, which is based on their personality. More importantly, a Pokémon’s Nature has a noticeable effect on their stats, which can slightly influence how they perform in battle. Natures are randomly assigned when you first obtain a Pokémon and cannot be changed. You can see a Pokémon’s Nature in the first page of their summary screen.
Altogether, there are 25 possible Natures, each granting a 10% increase for one stat and a 10% decrease for another stat. When checking a Pokémon’s detailed information, the increased stat will be highlighted in red, while the decreased stat will be highlighted in blue.
Of the 25 Natures, 5 of the Natures do not increase or decrease any stats (since the two effects cancel out). For these Natures, there won’t be any red or blue stats shown in the detailed display.
Above is a chart that outlines the increased and decreased stats for each Nature. The ones along the middle diagonal line are the “neutral” Natures that do not increase/decrease any stats.