2001A&A...366..100S

We present an analysis of the color variations of the X-ray binary V Sge during high, medium and low state of its activity over the years 1995-1997, using UBV data. We resolved the track of V Sge in the color diagrams (B-V and U-B versus mag(V)) during transitions between the states and show that the color variations on the orbital time scale are significantly smaller than the changes caused by the long-term activity. The mean B-V decreases by 0.15 mag during the upper part of the transition (brightness higher than 11.5mag(V)) from the low to the high state but stays almost constant below this level. On the contrary, U-B does not change significantly during the whole transition. Comparison of our data with those of Herbig et al. (1965ApJ...141..617H) shows that although the character of the long-term activity in V Sge changed significantly during the last decades (Simon & Mattei, 1999A&AS..139...75S) the colors and their variations with the brightness level remained similar.