There are 2 potential issues which can cause this to happen:

Lack of the CEP

1. If you are not generally in the habit of downloading custom furniture or you have never downloaded furniture for your Sims 2 game before then you will need to install a copy of the CEP. The Color Enabled Package is an extra file for your game that tweaks it so that custom furniture can be displayed properly. You can find more information about thise file here in our FAQ or you can go directly to the official CEP home at ModTheSims2. 

You can install the CEP repeatedly so if you're not sure if you've added it already then there's no harm in installing it again!

Often we find people forget to reinstall the CEP after adding a new Expansion pack - if you've just upgraded your game but forgotten to install the CEP again then make sure you download and install the latest version.

You should not need to reinstall the lot or remove instances of it placed in your neighbourhood - it should automatically update the next time you play after the CEP repairs your game.

Missing Repository Items

2. If your CEP is up to date and correctly installed and there are only 1 or 2 items on the lot which are blue and other custom furniture is showing correctly this is usually the result of a missing repository item.

One or more of the objects they've used on the lot borrows its textures from a different object which the house builder has in their game but which wasn't placed on the lot and therefore included in the lot package. Its hard to tell which items behave in this way so its an easy mistake to make unless the house builder is very strict about keeping records of such associated files and if the object artist was kind enough to make the link clear in the object description!

Whilst its a problem that we are certainly trying to tackle here as the number of repository objects created by the community is on the increase, it is difficult to keep track of them all. If you experience this problem then the best thing to do is either to delete the black and blue object from your game, or contact us so we can give you the link to download the respository 'master' object so its flashing blue slave will have a texture to use and therefore wont be flashing blue any more! 

We will also update the house zips to include the spare packages as and when we discover such problems but we can only do this if you help by making us aware of this. Same applies to other sites if you have this issue when downloading elsewhere - its not a problem most builders are likely to be hugely aware of since the objects appear to work as expected in their games!