Corners can be cut/knifed perfect, but depends on the shape of the inlay, and takes some practice to aquire the skill at that level. Some are alittle tougher to knife in. For instance, seems as if points with straight lines are easier to cut the corners in on, some inlays that have a curve in them are alittle harder to do. Sometimes dyes are used, but not usually to cover up anything major. The materials you are knifing can play into It also, some materials are easier to knife in then others. Sometimes inlays can go in, and fit nice and tight, but still have the slightest bit of glueline in the end, so some prefer to outline in black inlay, and use a died epoxy to glue them in just to be safe. It's nothing more then tools of the trade.
Here is an example to give an idea, the cue pictured is just a basic house cue conversion I was practicing on, but gives an idea. These somewhat simple inlays did not need the dye, but It was used after the pics were taken just to be safe. sorry have not turned It down yet, so don't have the finished pic. The second picture shows the pocket after being cut with a pantomill, and still has round points/tips. The first picture is after being knifed in to sharpen the corners. The third is the inlays fitted to the pocket, but unglued. As you can see, they probably would be fine without the dye, but made more since to use It to be safe, and since it was black anyway it was used when they were later glued in, just as a safety precaution on this one. Notice the straight lines on this inlay- That makes It easier to knife the corners in IMO. To give credit where due, Chris was kind enough to sell me the pattern for this, It was close to what I wanted anyway, and made more since to get It from him then to make My own being It was almost identical to what I wanted in this design. His patterns work very well. I have others I made Myself that have curved lines going to a point as oppossed to the straight, and they are alot harder to knife the corners in on.
I just wanted to clear the air on the dye issue, so people don't get the wrong idea about what makers are doing this for. Most do not fill any huge gaps with It, in fact probably don't even need It in most cases. The inlays still fit tight, just like one would expect. I am just a rookie to alot of makers standards, but even I did'nt really need the dye here, just alittle extra assurance for Me to be safe, since it was in black anyway.
Greg