QUOTE (envision)
The version I am using is Bryce 5.5
OK, thanks, I have installed 5.5 so I can post screen shots to help.
There are many option to create sky`s. So lets start with a preset and work from there.
Open Bryce: Select Sky&Fog (on the top menu), then click the little triangle next to this,

This will bring up the sky presets. There are quite a few that you can chose from as a starting image.

Once you have a preset that is close to what you want, we can then edit this.
To reposition the sun: Hold down the "Ctrl" and "Alt" keys (keep these held down) then double left click on the sun control (number 1), then, while still holding down the "Ctrl" and "Alt" keys, left click on the screen where you want the sun to be (Number 2). As long as you hold down the Ctrl and alt, you can click on the screen until you get the sun in the posistion you want.

From this quick edit, the result is not too bad

You can edit the sky color from the top menu (top left edit window), just left click (and hold the mouse button down) will bring up a color swatch,.. there are 3 colors you can change.

There is an option to change the Frequency/Amplitude of the cloud on the top menu (see pic), just left click in that window (hold down), then move the mouse left/right up/down.
Here I have just changed the colors and the Frequency/Amplitude of the preset.

The other small images on this top menu allow other editing to be made, such as "Ambient color", "Fog", Haze", "Cloud hight" etc. Just move your mouse over the image, and if you look bottom left, it will show what option you have, you can then left click (hold) and move the mouse to change the setting.
I have to go for now (work), but will post more info later.