We present the fiducial main sequence stellar locus traced by 10 photometric colors observed by SDSS , 2MASS , and WISE .
Median colors are determined using 1,052,793 stars with r -band extinction less than 0.125 .
We use this locus to measure the dust extinction curve relative to the r -band , which is consistent with previous measurements in the SDSS and 2MASS bands .
The WISE band extinction coefficients are larger than predicted by standard extinction models .
Using 13 lines of sight , we find variations in the extinction curve in H , K _ { s } , and WISE bandpasses .
Relative extinction decreases towards Galactic anti-center , in agreement with prior studies .
Relative extinction increases with Galactic latitude , in contrast to previous observations .
This indicates a universal mid-IR extinction law does not exist due to variations in dust grain size and chemistry with Galactocentric position .
A preliminary search for outliers due to warm circumstellar dust is also presented , using stars with high signal-to-noise in the W3-band .
We find 199 such outliers , identified by excess emission in K _ { s } - W 3 .
Inspection of SDSS images for these outliers reveals a large number of contaminants due to nearby galaxies .
Six sources appear to be genuine dust candidates , yielding a fraction of systems with infrared excess of 0.12 \pm 0.05 % .