I came cross an interview with James Morris, the director of the World Food Programme, published last 19 of July (2003).

The WFP is a UN agency that coordinates emergency food deliveries in those countries and regions where hunger is a major problem and the states have no means to provide this aid themselves. It has a site at http://www.wfp.org where you can find more information.

The interview came illustrated with a photo of James Morris in front of a cloth, presumably a flag, bearing the organization's symbol. The site, however, shows the same symbol but with a different sigla. Where the picture has PAM, the site shows WFP. The site also shows the symbol on different backgrounds and in different colours. So what are the colours of the flag? The answer needed some digging, but at http://www.wfp.org/index.asp?section=7_3 one can find a picture of a high WFP official in front of a flag, in colour. It turns out that the flag is white with the symbol in UN blue.
Jorge Candeias, 28 July 2003

The sigla is usually displayed in the 3 main official languages, English (WFP - World Food Programme), French (PAM - Programme Alimentaire Mondial) and Spanish (PMA for Programa Mundial de Alimentos). For Arabic (the 4th official language of the organization), the name is displayed in full text.

Moreover, on the field, the flag usually has the logo on the left and the full name of the organization on the right, in the local language of the country of operation in order to guarantee the best visibility, but also security for the staff.
Carl Engelsen, 17 May 2010

I think it's important to keep in mind that using a WFP flag is not only for mere representation but is also largely motivated by practical reasons (what I called in my last message "visibility and security on the field"). This remark also applies to other UN agencies or NGOs. In this extent, it explains why language changes depending on the context and why full name is most often used on the field whereas the logo and acronym are enough for "administrative" context. Also, I would say that it's not directly the flag that firstly embodies the organization but the logo (also widely used on vehicles, compound gates, planes, items distributed, clothes, etc.), together with the blue and white colours.

For those reasons,
- All WFP flags display the logo,
- The logo remains unchanged, even on the reverse side of the flag,
- The lettering (either acronym or full text) is always readable, on both sides of the flag.
Concerning this obverse/reverse issue, I actually think that it does not really differ from the general rules for flags with writings, as explained at xf-twos.html.

I would consider the version displayed here with "WFP" acronym in English and the logo at the centre as a kind of "official" one. But flags used on the field seem to be rather conceived on a case-by-case basis. For instance, the "Haitian" flag proposed by Peter has the acronym both in English and French, perhaps because it is an important operation with international media coverage, which requires to maintain visibility in English. When I was working in Nicaragua with WFP, we had flags with the logo on the left, the acronym only in Spanish (PMA) and "Programa Mundial de Alimentos" in full text on the right. The reverse was empty. I also have a flag from Haiti which is exactly the same, with the reverse empty, except that with both acronym and name in French. I have a picture from Chad where there is just the logo on the left, without acronym, and the full name in French on the right. I also found a photo on WFP website where the flag is only in Spanish, with the internet address displayed. On this photo is it the reverse of the flag that is shown and it looks as if the producer had just printed the same pattern on both sides of the flag, so on the reverse the logo appears at the fly.

Concerning the Arabian version, it seems less common than other versions and I was not able to find pictures, although I am pretty sure I have already seen some in the past. Thus, considering the variety of flags displayed by WFP teams, my guess is that those flags are designed in the respective countries of operation, following what WFP staff/local producers are used to use/make, thus eventually coinciding with more general flag flying rules, but I cannot certify it. I'll try to make further research to find examples, and will obviously let you know!
Carl Engelsen, 28 June 2010