Use Compose Preview to Show your Theme

colors.kt

package com.dladukedev.themetest.ui.theme

import androidx.compose.foundation.background
import androidx.compose.foundation.layout.Box
import androidx.compose.foundation.layout.Column
import androidx.compose.foundation.layout.size
import androidx.compose.material3.Text
import androidx.compose.runtime.Composable
import androidx.compose.ui.Alignment
import androidx.compose.ui.Modifier
import androidx.compose.ui.graphics.Color
import androidx.compose.ui.tooling.preview.Preview
import androidx.compose.ui.unit.dp

val Red = Color(0xFFFF0000)
val Green = Color(0xFF00FF00)
val Blue = Color(0xFF0000FF)

@Preview
@Composable
private fun ThemeColorsPreview() {
    Column(verticalArrangement = Arrangement.spacedBy(8.dp)) {
        ColorBox(color = Red, name = ::Red.name)
        ColorBox(color = Green, name = ::Green.name)
        ColorBox(color = Blue, name = ::Blue.name)
    }
}

@Composable
fun ColorBox(color: Color, name: String) {
    Box(modifier = Modifier
        .size(48.dp)
        .background(color),
        contentAlignment = Alignment.Center,
        ) {
        Text(text = name)
    }
}