As a closer inspection revealed yesterday, the Premier League does not allow teams to have more than three different kits per season. To avoid possible kit clashes with "just" three kits, the Premier League has another very strict rule.
Premier League Kit Contrast Regulations - Each Kit of a Team Must Be Wearable Against Each Other With Sufficient Contrast
Under the competition's handbook rules and rule M.14. teams must use distinct tones across home, away, and third kits. Every kit "must differ visibly from and contrast with each other Strip".
Each Strip registered with the Board by a Club must differ visibly from and contrast with each other Strip registered by the Club in that Season, such that they could be worn by competing Clubs in a League Match, for the purposes of Rule M.22
Tottenham Hotspur's 26-27 kit lineup provides an interesting case study in kit planning. Alongside their traditional white home shirt, Spurs and Nike unveiled a navy away jersey and a purple third kit. The club's alternate shirts do not provide a contrast most people would find sufficient.
Indeed, the away match against Coventry is challenging for Tottenham's kit colors, but the purple third kit should work.
Premier League's rule forbids cases such as Bayern's two white kits in the 2023-24 season, and also Real Madrid's navy and black options of that same season.
Ultimately, match referees and league kit managers hold final authority over kit approvals before every fixture. While there is no rule barring specific aesthetic choices in isolation, having change kits that sit too close in tonal balance limits a club's versatility, occasionally forcing last-minute mixed shorts and sock combinations to satisfy contrast requirements on matchday.