What is the best resistor for red and orange led?
Define "best". What are the specs of your LEDs?
R = 2*(V-Vf)/If_max
For general indicator use with 3.3V and 5V I use 470 ohm. It's bright enough and minimises current draw.
You should use resistors with red base color for red leds an orange ones for orange leds - otherwise it just does not look cool. Imagin blue resisors for red leds ... that does not work.
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You can check the LED datasheet for its rated voltage & current. Note that the current rating is usually the maximum allowed and you can run it lower for less brightness.
If you don't have the datasheet you can estimate the voltage based on the color and calculate for 10-20mA. Then increase the resistance if it's too bright.
If you want the same apparent brightness from two (or more) LEDs, you may have to experiment. In general, you should increase the resistance on the bright one, because reducing the resistance on the dim one to make it brighter you may end-up with excess current, "stressing" the LED and/or Arduino.
Why 2 times?
My opinion of "best"
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