I have been trying to install the weather service, but could not get it to work. I went though the forum reading the posts and finally got it to work. It seems that many people are having the same issues. Hence, I am posting this mini guide which worked for me:

Install instructions:
Install NextGen Weatherservice apk.
It will install two apps: WeatherNextGen and Weather service

Put in UX folder these 2 files: (files for pongo skin)
weather_ng_pongo.zip
scheme_sky.zip

Unpack and copy in Scheme folder:
Scheme.zip
scheme_sky.zip for Non FHD screen resolution.
or
scheme_sky_FHD.zip for FHD (1920x1080) screen resolution
Note: add only one schemes version according to your phone resolution.

Start the WeatherNextGen app, go to settings and Enter the path for iGO NextGen (it may be /mnt/extSdCard/iGO_Avic or /storage/extSdCard/iGO_Avic (case sensitive)
Choose Imperial for F, or metric for celsius
When you run, the app, It should create file weather.txt in save/profiles/01/userlists. If it is not created, it means the Avic folder path is incorrect in the app

Now Start the iGO NextGen, go to Settings > Weather > Choice Sky > on

It should change the skies to reflect the weather

Now you can run Weather Service app to run the weather service and automatically start the iGO NextGen

To get correct appearance of sky, Weather service should be on. Otherwsie, appearance of the sky goes back to Default Day Colors

Hope it helps for most people.

Thank you to all the developers for their hard work.