What you see on the camera's LCD is pretty much irrelevant. It is an uncalibrated and not color managed display of a jpg processed by Canon firmware. There is no point of comparison to a monitor showing a preview of Adobe processing in a color managed app (Lightroom). Of course, unless your monitor has been calibrated and profiled the color management may be somewhat lame, depending on what generic profile the OS chooses. Moreover, if you are processing photos for the web, eBay or whatever, you can have no control over what others are seeing. All you can do is satisfy yourself that you have done your best.
I always shoot RAW and use the flash WB setting in camera since I just use 2 Yognuo strobes
I wouldn't do it this way. The camera's Flash preset is tuned to fit Canon flashes, the Yongnuo flash tubes may have a different color. And for some Canon flash + camera setups the two communicate and because flash color changes as flash duration changes, the Flash WB is altered accordingly.
I would use a certified neutral grey card and insert it into a shot at the subject location and later use that shot to set the WB in Lightroom with the eyedropper probe.
the black items have a slight bluish tint
In the Calibration panel, try using the Shadow/Hue slider which will modify the way that the selected profile renders the dark tones. Or alternatively, the Split Toning panel.
