My apologies for missing this post, I'll have to ask around and see if I can find someone that knows anything about this Forum. ;>
So, to break it down, you have two questions here:
• Why yellow vs. white mesh?
• Is 130 mesh OK vs. 137 for powder printing?
Let me start out by saying that you will be perfectly fine using a 130 mesh, white screen so you can relax and keep rolling.
That said, let's take a look at why we choose the 137/yellow as optimal.
Yellow vs. white mesh:
The issue here is not about the mechanical properties of the mesh but how it handles exposure to ultraviolet light to set your image in emulsion.
A white mesh (clear filaments) can conduct full spectrum light so it will tend to pipe UV light beyond the edges of the open areas in your film when on the exposure table and thereby set a slightly larger area of emulsion than you intended.
Yellow mesh, by virtue of its color, filters out UV light so it should expose a more accurate stencil. There is not a huge difference but every cumulative thing you can do to enhance accuracy helps.
130 vs. 137:
@jdepaula is right-on here in that it will yield a slightly lower resolution image. Please be sure to adjust your halftone lpi to support this lower res.
From the lesson you'll remember:
Maximum LPI = 1/4 screen mesh TPI
So, for a 130 mesh screen your maximum LPI will be 32.5 vs. 34.25 for 137 mesh.
The other item to be aware of with a more coarse mesh is that it will deliver the powder at a faster rate and allow some larger particles to get through. Again, not a bad thing per se but it is different from what we demonstrate in the lesson.
Also as @jdepaula mentioned, Midwest is a great dealer if you do want to track down the 137 mesh yellow screens.http://www.midwestsign.com/