There are articles on many types of LED, and yes different color when mixed can vary the current rating on the lowest color part (potential overload when wired in series)
That board, looks to be two layer. Have to trace the paths to each LED, resistor connection, as the board is giving direction via being labeled topside. Then from the LED common onto where ever else.
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LED calculators exist online.
--------------------- --:Edited:- -Rant does not fit properly, so just some extra info Section below.
The LED voltage forward drop is needed mostly (if obtainable, some multi meters do not even show some LED's are there at all even if it is lit), then the desired voltage and its current capability (so not to drop its output via too much current draw) then the desired LED current, per LED. then finally how many connected in rows of series configuration.
Meaning so many number per row then on to the next resistor chained row (each row has its own deticated resistor in a multi row config), or an single row with a primary resistor could be done.
Different LED and size types and current ratings as with many types, 3mm are usually low current 10mA, tho can be made for higher current/Volt. And 5mm avg 25-30 mA max unless high power, then the rating just keeps on going like an 10W 900LM lamp bead that has 9 small LED cells in one casing that can harm the eyes.
Current rating can usually be determined via the size of an led for a starting point (which can vary and I am not completely aware of ratings for an unknown LED without an known datasheet that is not all ways possible to obtain a datasheet without knowing the LED such as those on that board per example).
However those types (on board) are usually bright type, as for high visibility and for an market view point there are countless types of LED's to a point of eventually hitting reality and eventually having an real number of how many types exist would be quite a chore.
My meaning is there are thousands to choose from with Volt/Current ratings.
The diode acts as an forward drop limiter as voltage can change on a vehicles electrical system via alternator and other electrical systems flooding random GND points, if I've gotten that correct. And can usually be located at the end of resistor rows before connection to the Common GND as appears on that board for most view point.