Electronic – It is possible to exist more than 1 color code for same resistance. Can i use all of these color-codes

How do I talk about what the resistor is doing?

In this case you call the resistor a current limiting resistor, because it's function is limiting current to the diode.

Do I say that the red LED needs less current than the green LED to glow as brightly, so it has a stronger resistor to reduce the current?

There is no way to compare a red led with a green led, there are several factors at work when you look at an LED including:

1) Human eyes assign diff the brightness of different frequencies differently, here is the response of a human eye, we see green really good. Source: NPL

2) The LED's have different efficiency curves and have different voltage drops and have different intensities. Red is more luminous than green, but to the eye green has an easier time showing up.
Source: LED magazine

Or do I say that the red LED needs less voltage than the green LED to glow as brightly, and the resistor soaks up voltage because of V=IR?

You could say, the red led needs less voltage for the same amount of current because its voltage drop is lower than a green led. But voltage drop and current have little to do with how bright an led is.

Source: LEDnique

I made on my Arduino Uno some MIDI in/outs, but never seen some color scheme.

The MIDI ports have specific numbers (which are not so intuitive). And also check good what is the front and back.

Btw, MIDI is far from obsolete. Every synth still uses them (although USB MIDI is getting more popular, a lot of music devices with with DIN5 MIDI plugs). MIDI cables can be found at every decent music shop.