Some airlines, Delta in particular, have dark underbellies on their liveries. Is this only aesthetic or is there a purpose for it?
6$\begingroup$ Perhaps it hides dirt better? $\endgroup$– Dan PichelmanFeb 20, 2014 at 15:25
7$\begingroup$ I have heard that it helps the airplane stand out more when looking up at it from below because it contrasts with the sky. This also applies to looking down at a white aircraft from above where it typically stands out from the ground (unless it is covered in snow. :) ). $\endgroup$– LnafzigerFeb 20, 2014 at 18:25
$\begingroup$ Emirates paints its logo on the ventral: fr.academic.ru/pictures/frwiki/69/Emirates_A380_2.JPG $\endgroup$– CalchasJun 15, 2015 at 15:30
Originally (way back before radar) the colors had a practical use for maintaining visual separation between planes, which was done by pilots looking for the other planes with their eyes:
Dark underbelly: Easier to see from below against bright clouds or sky.
Light top-body: Easier to see from above against (typically) dark ground.
The idea being that when you're looking visually for other civilian air traffic (or from the ground) one wants to maximize visibility without losing them in sky glare or ground clutter.
If you look at older military planes you'll often see the exact opposite (dark colors on top and blue on the bottom) because those military planes didn't want to be seen.
$\begingroup$ It should probably be noted that maintaining visual separation is still very common, especially for VFR traffic. While VFR traffic does typically (but not necessarily) still have at least Mode C transponders, it's perfectly common to fly around without ever even speaking to ATC if you're not in or near controlled airspace. This, of course, is not true for airliners, which generally stay almost exclusively in controlled airspace. $\endgroup$– reirabMar 23, 2015 at 20:38
$\begingroup$ @reirab - Yup, I've done VFR separation and called out 'I have the traffic in sight' many, many times. :) $\endgroup$ Mar 23, 2015 at 22:16
Aircraft are generally a nice bright white. Aside from the company logo, this leaves the other company colors needing a space. The tail, engine cowlings and underbellies are the more effective places to put it. There is color on the tail, color on the bottom, and the logo in between.
In my opinion, the lower one lifts forward the identity of the company much better.
9$\begingroup$ The 747 in your first picture is an outdoor museum exhibit: it's not at all representative of the condition of commercial airliners. $\endgroup$ Mar 21, 2014 at 3:06
1$\begingroup$ @DavidRicherby: And on top of that, the dirt on that airplane was certainly not splashed up from the nosewheel. It has the same intensity along the full length of the plane, and it is running down from the windows, probably washed down by rain at wherever the plane is permanently located. $\endgroup$ Mar 23, 2015 at 22:08
$\begingroup$ ...and that is in Musée de l’Air et de l’Espace in Le Bourget, near Paris. Wikipedia $\endgroup$ Jun 15, 2015 at 13:57