Making a further change - How to use the random value function with an argument?

I am having difficulty with tweaking the solution further for the sake taking my understanding further. I would like to make the randomValue function reusable so that it uses a parameter instead of the fixed value of 256.

Original Function: As per the lesson the function is:

function randomValue() {
    return Math.floor(Math.random() * 256);
}

Revised Function: The function I would like to use:

function randomValue(upper) {
    return Math.floor(Math.random() * upper);
}

I have been wracking my brain with this one but I cannot seem to make what I believe should work ... to work:

for (let i = 1; i <= 10; i++) 
    html += `<div style = "background-color: ${randomRGB(randomValue(256)} " > ${i}</div> `;
}

PS. There are a few things I discovered while trying to figure the above out: Making the Circles Greyscale To have the same random number applied to the red, green, blue channels so that each circle is displayed in greyscale I removed the parenthesis after the word 'value' in the return statement and added parenthesis after the word 'randomValue', the argument in the html statement in the for loop.

function randomRGB(value) {
    return `rgb(${value}, ${value}, ${value})`
}

for (let i = 1; i <= 10; i++) {
    html += `<div style = "background-color: ${randomRGB(randomValue())} " > ${i}</div> `;

Important Update:

I have got closer to the solution, I can use the randomValue function with an argument randomValue(upper) but I can only get as far as greyscale with the bonus of being able to limit how brightness of the circles in the html. The example below will show 10 circles varying between black and very dark grey.

let html = '';

function randomValue(upper) {
    return Math.floor(Math.random() * upper);
}

function randomRGB(value) {
    return `rgb(${value}, ${value}, ${value})`
}

for (let i = 1; i <= 10; i++) {
    html += `<div style = "background-color: ${randomRGB(randomValue(50))} " > ${i}</div> `;
}
document.querySelector('main').innerHTML = html;

If you read this far, thank you! And if you have a solution that produces full color circles as in the original whilst using my revised function with argument i.e. randomValue(upper) please let me know.

Thanks all,

Shane