Use ContextCompat.getColor(context, <color>) to get colors in your Android project.

Sample code to test this methodology to get colors.

package com.bitcolon.canvasdemo

import android.content.Context
import android.graphics.Canvas
import android.graphics.Paint
import android.util.AttributeSet
import android.view.View
import androidx.core.content.ContextCompat

class CustomView @JvmOverloads constructor(context: Context, attrs: AttributeSet? = null, defStyleAttr: Int = 0) : View(context, attrs, defStyleAttr) {

    val paint: Paint = Paint().apply {
        // get color
        color = ContextCompat.getColor(context, R.color.purple_700)
        style = Paint.Style.FILL
    }

    override fun onDraw(canvas: Canvas) {
        super.onDraw(canvas)

        override fun onDraw(canvas: Canvas) {
            super.onDraw(canvas)
            canvas.drawCircle(100f, 100f, 100f, paint)
        }
    }
}