monitor displays back background on only one web site

[mahesh]

When I browse on different websites the background is always white with black printing. Recently on only one site ( one that I frequently use), the background changed to black with white printing. At times it is difficult to read. No other sites have changed. I inquired at this one specific site and they claim they have made no changes although the overall format has changed.
I can't find anyone with a similar problem and fail to understand why this is occurring on only this one site