I'd like to take the boring white LED bulbs out of my solar garden lights and replace them with colored LED lights. Here are some advises.
LEDs have something know as the forward voltage. This voltage is dependent on the particular LED you are using, but they tend to be related to the color. Generally, Red, Orange, Yellow and Green tend to have lower forward voltages (1.6V - 2.2V), while Blue, Violet and White tend to have a higher one (2.5V - 3.7V). Note that individual models can be different, and high brightness LEDs can be higher.
Any circuit designed to drive an LED has to be setup so that the right forward voltage drops over the LED, otherwise you are driving it with too little or too much current. There are different ways to drive LEDs, the simplest being a current limiting resistor. The solar garden lights I've looked at did it that way, but some models could be more sophisticated.
If you replace the LED with one with a similar forward voltage you should be fine. If it has a different forward voltage, you could be over-driving it and possibly burn it out.
Without knowing anything else about the circuit, it's hard to tell, but I would think you might have a better chance replacing the white with a blue LED than one of the other colors (Red, Orange, Yellow, Green). If the circuit simply uses a resistor, you could of course replace that with the appropriate valued resistor for the LED you are using. Or you could simply try it out and see how long they hold. It's possible that you are over-driving a red LED, but it will live long enough for the burn.
Here's the deal with solar garden lights:
The circuit isn't like those simple battery + LED + resistor circuit that you have to set to a specific value to work. The solar panel and the battery don't provide much voltage, but the white LED needs a higher voltage to work. So the lights have an oscillating power circuit in there that converts the low-voltage from the battery to a sufficient voltage for the LED, along with some current. It's relatively efficient, which is definitely needed for those solar lights.
What does that mean for you? You'll just have to see if it works by experimenting. The circuits can usually "auto" adapt to the different voltage drop from the color-changing LED. So there's a good chance the auto-color-changing LED might just be a drop-in replacement for the white LED. Whether it uses more power or all the colors of the lights work... well, you'll just have to see.
How to do it? Rewire the white LED with the color changing one.
For myself, I'd probably end up just building something that would do the same thing because those solar garden lights are relatively expensive for what you get. It gives me an excuse to buy a bulk amount of parts too.
LED's are pretty robust devices and you've got to work hard to zap them! I have seen them massively over-driven and still working.
I've just taken one of my lamps apart and it has a very crude regulator between the solar cell and the LED. LED's are polarity sensitive so you have to solder them into the circuit board the right way round. If you look inside of the plastic LED envelope the lead that ends with a bigger metal tab is usually the Cathode which has to be connected to the negative supply. Often the cathode is also the shorter lead. Before you unsolder the original LED check which is the cathode using the same method.