I was told it had to be bright white light, to make sure their eyes dilate, but when I checked my power suns give off bright pale yellow & they've been fine under those for 6 years. I would see if you can get a light that gives off bright white, did you get your basking locally or over the internet?
The reason you want a bright white light (in the 4000-5000k range) is because this is close to mimicking the color temperature of the sun. Obviously at noon, the sun has a bit more of an intense Kelvin range, but 4-5000k is what you should shoot for in your tank.
A yellow or soft white, is usually around 3000-3500k.
Ultimately, it's not the biggest deal in the world. A 3500k bulb will still protect the eyes, although I have no facts to prove that a higher Kelvin would do better. Not to say I couldn't dig up some research for you, I just simply do not have the time currently, and thought i'd chime in real quick. The higher energy of a higher Kelvin light, should protect the eyes better. It's just like I said, I have nothing to back that up at the moment besides my own understanding of it.
In addition, the yellower a light (to a degree) the lower it's Kelvin rating.
The whiter a light (to a degree) the higher it's kelvin rating.
You won't be dealing with anything above 6000kelvin in your bearded dragons tank, which is why I make no mention of blues and reds.
Here is a nice little visual for you, and anyone else.
I've had my girl under a 100w clear, standard household bulb which gave off 2700k for over a year now, recently switched to a halogen flood light with 2900k. Are both of these bulbs insufficient? Should I buy a new bulb with a higher kelvin rating? will the current flood light affect her negatively? She's very lively and alert so I thought everything was okay. any thoughts on this would be appreciated greatly. thanks everyone