Multi chamber profiles create an insulation barrier of air that reduces the transmission of cold to heat. The optimal window profiles use two and preferably three chambers between interior and exterior faces. The multi-chambered profiles also increase the strength of the profile tremendously over a solid extrusion by increasing the surface of welded seam.
A typical welded profile will yield between 9 & 20 inches of welded seam. Some multi-chambered designs offer as much as 25 inches of frame and 14 inches of sash weld seam. This results in a weld that is stronger than the extrusion itself. Some manufacturers used to offer windows with mechanically fastened corners instead of welded. These would invariably separate early and begin a freeze-thaw attack or heat induced expansion that would shorten the life of the window and reduce its thermal performance. Avoid any mechanically fastened or glued corners. Always opt for a multi-chambered, welded corner window.
Primarily, vinyl windows were offered only in white. This was to keep the cost down, but it was also to prevent obviating the issue of fading and color degradation. Over time, white PVC will become yellowish with age. Some extrusion manufacturers counter this by adding some blueish color to the polymers to balance this out. If you are driving around, and see some vinyl windows with a sickly looking yellow cast these were probably lower cost extrusions and you will see the result.
Additionally, the UV is the light spectrum most affecting the color degradation so the higher your altitude, the faster the process of color degradation will occur. Some manufacturers now offer a rage of colors including darker browns. Be very wary of darker colors, especially at higher altitudes (Rocky Mountain Regions) as you will likely see a rather quick degradation of the color. There just is not a long enough history with darker colors under longer term exposure to intense UV. PVC formulations are improving, but more time is need to judge the effectiveness of the color imparting materials before taking the plunge.
That said, I have seen some beige colors under service for several years in the Colorado region that seem to be holding up quite well. One final caveat, PVC is subject to becoming brittle under long term exposure to high heat as in a desert environment. In these areas it is critical that you get a high quality, multi-chambered extrusion to counter the effects of long periods of exposure to high heat.
The most attractive feature of vinyl windows is their low maintenance. Vinyl windows do not require any exterior maintenance other than washing. Do not paint them; ever, the chemicals in the paint will likely reduce their longevity…and your neighbors will want you drug-tested.