Q.plants turn pale and die
Why would plants turn very pale and shrivel up and die (tomato, Brussels sprouts, peppers)?

I am going to need a little more information. Are these plants in the ground outside (if so - were they just recently planted?) or are they seedlings currently being grown inside? If they are outside, what has the weather been like? Really rainy? Really cold? - what have the lows been?
How often have you been watering them? What kind of light/sun are they receiving?