In brief: Not exactly. Blood actually doesn't get thinned.  what we call blood thinners are agents that decrease the ability of the blood to clot, usually used in people whose blood clots excessively.
Taking B-complex vitamins, which include vitamin B12, can cause urine to have a bright yellow or even orange color, but check with your doctor to be sure that's what is going on in your case. B vitamins are water-soluble vitamins, which means that what your body doesn't use is excreted in your urine. Riboflavin (vitamin B2) is especially likely to cause this color change in urine. Several medications can also turn urine a bright yellow or orange color. Changes in urine color may also signal certain health problems.
Quote: Taking certain oral medications can turn your urine anything from fluorescent green to blue, and eating carrots can give it an orange hue. The consistency, odor, and color of your urine are often indicators of your lifestyle and health condition. Each of these signs can vary depending on what you have been eating and drinking to medical diseases. Your urine gets its yellow color from a pigment called urochrome. That color normally varies from pale yellow to deep amber, depending on the concentration of the urine. Taking certain oral medications can turn your urine anything from fluorescent green to blue, and eating carrots can give it an orange hue.