The use of yellow silkscreen in making PCBs is gaining momentum because it allows for easy routing to take place. When working on this boards, you will notice that the contrast between the traces, the planes, and the spaces will be relatively high and the resulting artwork will be attractive. Unlike the white silkscreen which does not contrast well, the yellow silkscreen allows you to do the routing easily and is easy to clean. Even though, it is important to note that most people do not prefer working on a yellow silkscreen because it is always murky.
Note that PCB silk-screen can be used on components to help identify warning symbols, company logos, and test points. Silkscreens are always required on the soldier side since they use specifically formulated inks.
If made by the PCB manufacturers, they are required to provide identifiers and manufacturers mark that allow for tracing. Unfortunately, there are no standards to be followed when placing the marks. Most manufacturers try to place them in areas they consider noncritical. However, if you want the marks to be placed in distinct areas, you need to communicate this to your manufacturer and specify this in PCB readme.txt files.
On the other hand, it is necessary that you use solvent emulsion to coat the screens to allow for stretching. The emulsion coats the screen before imaging is done. If you choose to make the yellow silkscreen, you need to consider some parameters such as the ink to be used, the humidity, the room temperature, hardener and line resolution. You also need to double check the ident layer before sending your final design for fabrication.