Using the First Valid node

First Valid allows you to handle possible graph evaluation errors by providing alternative branches.

For example, here’s how you’d set up a compound to use either an attribute value or a value entered in the compound PPG. In this example, the PPG value is the fallback: if the attribute is not set, the value from the PPG is used.

Here’s another example. If there’s a texture map on the object, First Valid will pass through the texture map color. Otherwise, solid black is used.

Note that you don’t need to keep the constant color node. You just need it to force the type (Color) of the First Valid node.
After that, you can simplify to this:

Time FX for iPhone, iPod touch, and iPad on the iTunes App Store

Time FX is a cool, attractive clock App for iPhone, iPod Touch and iPad that uses Jos Stam’s amazing fluid dynamics solver to emit the current time in dynamic and interactive ways. Time Fx features both analog and digital effects, alarm functions (including the ability to wake to your own iPod playlists),  and a ton of themes to choose.  You may never leave your iPad sleeping again.

via Time FX for iPhone, iPod touch, and iPad on the iTunes App Store.