guitars

Get yourself an actual metronome, a mechanical one. That has a strong visual indicator.

A mechanical metronome will help with a visual indicator, but this smells like a classic XY problem to me. Your issue isn't that you need a visually distinctive metronome, it's that you are rushing the beat and need to break that habit.

Sadly, a metronome can only get you halfway in that endeavor. The real fix will be to practice with other musicians who can call you out on it in real-time. It is embarrassing, it is time-consuming, and it isn't fun, but it WILL break you of the habit and force you to play better. And make sure they call you out on it immediately. As in you do not get to continue the song once it is noticed, and you must start over like dying in a video game.

I don't know of an app for that, but it is worth improving. If you can't find an app that does what you want, try simplifying what you're doing until you know you're locked in with the metronome. Just simple strumming on every click and nothing else. Even eliminate the guitar entirely if you have to and tap on your desk or something. Then gradually add complexity back in while making sure you're locked in at every step.

There's also an exercise I remember Victor Wooten talking about where he would have a click track or something to that effect that would cut out for a measure every once in a while. The idea is that if your timing is good enough, you'll be on the beat when the click comes back in. You could set up something like that in Garage Band. Make the gap small at first and then gradually increase it.

Use a DAW (digital audio workstation) app to record yourself playing. When you set the tempo it will create bars for the subdivisions. You can match that to the audio spike that indicates the notes peak. When recording music this is the method used to ensure the music is keeping tempo and the audio engineer may shift the audio stream to fix mistakes during recording.

GarageBand, Ardour and Reaper are all free DAWs.

Download pro metronom on the google play store, its a great metronome and I highly recommend it. But this won't fix your problem alone. I play CG and learned that we humans have a built in metronom the only thing you need to do is when in 4/4 speak 1 & 2 & 3 & 4 & 1 & ... So on on the beat of the metronom loudly. Now when you can do that start playing slowly.

Start slow and bump the beat ever so slightly to increase speed over time. Be aware that it might take weeks before reaching your desired speed depending on your skill and complexity of the score. But if you count out loud as I said you will have no problem of attaining the correct ritme.

I think your best course of action is to just keep playing to the click. You're always going to be wavering in time around the beat. Its not possible to play like a robot.

Progress might take longer than you'd expect. Just stay the course and enjoy the instrument more than anything. The fact that you care about being in time is a win.