Hi! Fineliners of other colors are fine to use, as long as they're not a color that makes the lines harder to see, like a very bright yellow, so you can still use those for future exercises if you want. Overall you've done a pretty good job so nothing to worry about! I'll go over the issues I've found though so you can keep improving, let's go!:

Starting on your lines you're doing a great job focusing on confidence over accuracy, and the accuracy is pretty good already as well! One thing that happens is that your lines sometimes fray on both ends. When drawing a line make sure you place the pen carefully at the starting dot so that lines can fray on maximum one end.

Moving onto your ellipses you're doing a pretty good job as well, I can clearly see you're focusing on making them as confident as you can on the exercises and you're succeeding even if sometimes the accuracy is a bit off, but just keep practicing like this and it'll get better!

Funnels are also very well done as well, the only thing that I want to point out is that in some ellipses you aren't alligning some ellipses to the minor axis. When the curves are off and keeping the ellipses within their bounds will make you draw a non symmetrical ellipse, then ignore the curves and draw it anyways. One thing that can also help is to draw the middle line after the curves so it's easier to make it centered.

Lastly on boxes you've done a good job as well, but I want to comment on a few issues:

-On rough perspective I can see you're getting a bit overwhelmed by having to draw lines inside the boxes as they get a bit wobbly, but remind yourself that every line is just the same as the previous ones done on the ghosted lines exercises. Start by drawing starting and ending dots, and approach them with the same mentality. When you're drawing a line forget about what line is part of, focus on doing the ghosted line exercise as best as you can.

-Another thing on rough perspective is that I see you're sometimes making the vertical and horizontal lines a bit tilted. On this exercise, all height lines will be perpendicular to the horizon line and all width lines will be parallel to the horizon line.

One thing that can help is that you can make sure that the lines have this relationship before drawing them, and if they don't have it then you can redraw the initial and ending dots as much as you want until you think it's correct. Doing it should make you get better results.

-Rotated boxes is a pretty good attempt! Most of the boxes are being rotated and you managed to keep most of the corners between boxes close. The only thing I want to comment on it is that sometimes you're repeating lines. No matter how off a line is don't repeat it, as repeating it will make the drawing look messier and encourage bad habits.

-On organic perspective you've done a good job too, but I think that you aren't planning all of your lines. Before starting a line no matter how small it is, make sure that you draw first its starting and ending dots, otherwise you won't be able to ghost it properly. Make sure you don't repeat lines in this exercise as well.

Perspective on the boxes is a bit off at times, but don't worry about it as you'll work on it on the box challenge.

Overall like I said you've done a good job so I'm marking this as complete. Make sure you don't repeat lines in the box challenge, and that you don't distract yourself from lines even if they're part of a box, like I said earlier, every single line is an individual ghost lines exercise, try to thing of them as one. Don't forget to do your warmups from on, and good luck with the 250 box challenge!