I will assume your color negatives were exposed correctly and show correct density (not underexposed). After that, printing needs to be done by either you or a custom color lab.

Anything with a machine print involved (whether it's a Frontier or minilab) will be only as good as the operator - which can range from good to awful. Most of what I see you could put in the closer to awful category.

I am lucky in that I have a custom pro lab that will do contact prints from which I can edit and then go to final custom prints when I want a wet darkroom color print.

I also have an Imacon scanner from which I can make digital files that I can take to a local lab with a LightJet. Lastly, I have an Epson 9800 if I want to make inkjet on rag paper prints.

The key to a good color print from a negative is to define what you want the print to look like (hand printed wet darkroom, Lightjet, inkjet) and then setup your workflow to get to that point.

Transparencies are easier judge because you know what the positive image looks like. Negatives are more difficult in that you need a proofing stage from which you can judge the image. 4x6 prints from a machine really aren't a very good proofing method unless they're from a pro level lab that takes the time to do things correctly.

My wife shoots negative film and drops it off at a local Walmart - and the prints range from good to bad depending upon which employee is working the photo area. Me, I take mine film to a local pro lab for development, then to another pro lab for proofing. But, I shoot medium and large format, she shoots 35mm and is happy with snappies.

If your images were washed out, and the film density is correct, then it's a printing problem. You need to investigate better print proofing alternatives which can include something as simple as a flatbed scanner so that you can do a digital contact sheet.

Let me also make the observation that one of the things I have done with wet darkroom prints is to make a color corrected inkjet "proof" that shows how I want the image to look in the final print. It saves time and gives the lab a visual guide.