You need to:

• Track the previous value (use the usePrevious hook)
• Compare it to the current value whenever the current value changes and use that to determine what colour to set it to
• Add a setTimeout function to reset the colour to the default after a second
• Handle the case where the value changes again before the reset has happened (by cancelling the timeout waiting to reset it).
• Cancel that timeout when the component unmounts (so you don't try to set a state that no longer exists).

Such:

import { usePrevious } from 'react-use';
import { useState, useEffect } from 'react';

const ChangingValue = ({ value }) => {
    const previous = usePrevious(value);
    const [color, setColour] = useState('black');
    const [timeoutId, setTimeoutId] = useState(0);
    useEffect(() => {
        clearTimeout(timeoutId);
        if (value > previous) {
            setColour('green');
        } else if (value < previous) {
            setColour('red');
        } else {
            setColour('black');
        }
        const newTimeoutId = setTimeout(() => {
            setColour('black');
        }, 1000);
        setTimeoutId('newTimeoutId');
        return () => clearTimeout(newTimeoutId);
    }, [value]);
    return <div style={{ color }}>{value}</div>;
};