I see a lot of people mistakenly thinks that if a user perfects Sage Mode learnt from Mount Myoboku, their markings will BECOME ORANGE. This is because Naruto is the first one to be shown perfecting it, and he had orange markings. NOTE: This speculation is based on the anime colouring only
Now let's think back, Naruto had orange markings BEFORE he even perfected it. At the same time, Jiraiya had red markings with the unperfected Sage Mode. That clearly shows that the marking colours are unique to the user
Another case is Minato, he was shown to have perfected it, but the tone of the colour in that scene is too hard to determine what colour it actually is (if you check the colour using a colour picker, you can see that the marking colours matches the flame colours on his cloak in that same scene and not Naruto's Sage Mode colour in a scene with the same colour tone)
Then there's Kashin Koji, which doesn't even have a coloured version. But it clearly looks identical to Jiraiya's Sage Mode markings (the two horizontal lines are blood used to summon Fukasaku/Shima, so they're not part of the marking). Since he's a clone of Jiraiya, it would make sense to assume the colour to be red as well
I know it might sound like a pointless speculation, but it's just good to know that they're unique to each user, which makes sense because every toad has their own unique designs