answer:An LED is a diode. As such it has a forward voltage drop, i.e., when it’s conducting current and shining light, there is a small voltage drop from one end to the other. (After all, with nearly zero resistance, its power consumption has to show up somehow—you can’t get something for nothing.) Different color LEDs have different forward-biased voltage drops. Blue is typically higher than other colors. So when different types of LEDs are wired in parallel, the current will take the path of least resistance (or least power consumption) and the current will not be the same through each device. In your case the orange LEDs are “stealing” all the current from the blue ones. The solution is to use a separate resistor for each LED in parallel, so the current is forced to divide more or less evenly through each device. Another alternative is to wire them in series, though this won’t work with only 3 volts driving 4 or more LEDs, because the total voltage drop will exceed the battery voltage. Even if the LEDs were all identical colors and ratings, chances are they wouldn’t conduct exactly the same current through each device & some would shine brighter than others. So it’s still best to give each LED its own resistor.