Display modes can show different things. For example, many different elements have glows or textures that are only visible on Fancy display. Let's run through these:

Velocity display

Velocity display shows wind speeds and positive pressure. Blue is up/down, red is left/right. Any combination of the colors is a combination of direction, so that diagonal wind lines are magenta.

Positive pressure is shown as green, which is essentially air that isn't moving.

http://img7.imageshack.us/img7/520/frame0000.png http://img840.imageshack.us/img840/525/frame0001.png

In velocity view, negative pressure is not rendered.

Pressure display

Pressure display shows the pressure value of the grid. Red is high pressure (can be created w/ AIR) and blue is low (can be created w/ VAC).

http://img691.imageshack.us/img691/7280/frame0002.jpg

Persistent display

Persistent display sustains elements' traces for a few seconds after they have left the location. It is useful to track motions, and also makes for a very nice effect on some saves (Spinning GRAV Colors is a good example). Essentially Motion Blur mode.

http://img135.imageshack.us/img135/4179/frame0011.jpg

Fire display

"Normal" display. Displays most effects, and includes heat-sensitive metal color changing. Does not include "fancy" effects such as fluid blurring, extensive glows, etc.

http://img135.imageshack.us/img135/5407/frame0012.jpg

Blob

Makes everything blobby.

http://img156.imageshack.us/img156/7933/frame0013.jpg

Heat

Heat displays different colors for different temperatures:

Absolute Zero (-273.15°C) - Blue

Sub-Zero (~-135°C) * Azure

Room Temp (22°C) - Dodger Blue

Warm (~150°C) * Light Blue

Very Warm (~600°C) * Cyan/Turquoise

Lava's Temp (~1600°C) * Electric Green

Hot (~2800°C) * Green-Yellow/Chartreuse Yellow

Red Hot (~3500°C) * Lemon

Very Hot (~4400°C) * Amber

Burning Hot (~5350°C) * Orange-Red

Scorching (~6200°C) * Scarlet

Blazing (~7400°C) * Ruby

Searing (~8400°C) * Deep Pink

Over Plasma (~9250°C) * Hot Magenta

http://img20.imageshack.us/img20/8862/frame0014.jpg

Fancy

Fancy displays different effects for elements. For example, Plutonium and uranium glow, and water has a more fluid-like appearance (both shown below) Photons also receive a glow effect and steam appears as a gray cloud with a purple lining. Introduced "fancy lensing" for Newtonian gravity (v53.1 beta). This "fancy" effect demonstrates how the path of light can be bent by dense masses (WHOL, BHOL and GPMP), the effect is most perceptively visual with GPMP, the light is so warped it creates an "event horizon" where nothing can escape.

http://img687.imageshack.us/img687/6195/frame0015.jpg

Nothing display

Nothing display only displays the element's true color - no effects at all are shown.

http://img91.imageshack.us/img91/9962/frame0016.jpg

Heat gradient

Renders particles with brighter or darker variations of their default color depending on their temperature, in such a way that heat diffusing through substances produces obvious waves.

http://img268.imageshack.us/img268/9261/frame0017.jpg

Alternate velocity

Renders X and Y velocity as white, but displays positive and negative pressure as red and blue just like pressure display.

http://img684.imageshack.us/img684/7335/frame0020.jpg

Life Display

Displays current life values of all particles in greyscale gradients. Similar to the waves in heat gradient view.

To get to it, you need to be in debug mode 'd' , You can then cycle through the displays to get to it. Its shortcut is shift-1 (only works in debug obviously).

From left to right; GOL, PRTI and FIRE.

http://img600.imageshack.us/img600/8961/lifea.png

Misc

Vine mode

press "t" to turn it on. When it is activated, vine will grow up and down WOOD.

Grid

Pressing "g" in-game will activate the grid function. There are nine grids varying in size.

https://lh3.googleusercontent.com/_pgh0ByMQCI4/TUoxqoh2f3I/AAAAAAAAASg/c4mBXF1b8Hw/s800/Grid.png