To change the color of a text in a Text Composable, pass a Color object to the color parameter. Note that this is a Color from the androidx.compose.ui.graphics package.

@Composable
fun Greeting(name: String) {
    Row {
        Text(text = "こんばんは!")
        Text(text = "$name!",
            color = Color(0xFF00FF00))
    }
}

The preview will look like this:

Use resource

If you want to use a color defined in a resource, use colorResource() .

@Composable
fun Greeting(name: String) {
    Row {
        Text(text = "こんばんは!")
        Text(text = "$name!",
            color = colorResource(id = android.R.color.holo_green_dark))
    }
}