Colors

The COLOR statement in QuickBasic allows one to change the text/background. The sixteen colors available are (names from QBasic Wikibook; hexadecimal from QB64 Wiki):

• 00: Black – #000050
• 01: Dark Blue – #0000A8
• 02: Dark Green – #00A800
• 03: Dark Cyan – #00A8A8
• 04: Dark Red – #A80000
• 05: Dark Purple – #A800A8
• 06: Orange Brown – #A85400
• 07: Grey – #A8A8A8
• 08: Dark Grey – #545454
• 09: Light Blue – #5454FC
• 10: Light Green – #54FC54
• 11: Light Cyan – #5454FC
• 12: Light Red – #FC5454
• 13: Magenta – #FC54FC
• 14: Yellow – #FCFC54
• 15: White – #FCFCFC

Circles

The QBasic Wikibook shows the CIRCLE command as follows:

CIRCLE ([X Coordinate], [Y Coordinate]), [Radius], [Color Number]

QB64’s Wiki shows:

CIRCLE [STEP](Column,Row), radius%, [color%][, startRadian!, stopRadian!][, aspect!]

Thankfully, when I posted this question on StackOverflow, wolfhammer provided a complex example including a reusable function to achieve the same effect with JavaScript:

var can = document.getElementById('can'); 
var ctx = can.getContext('2d'); 
var w = can.width; 
var h = can.height; 
var x = w/2; 
var y = h/2; 
var radius = 30; 
var startAngle = 0; 
var endAngle = Math.PI*2; 
var color = 'red'; 
CIRCLE(x, y, radius, color, startAngle, endAngle, .5); 
CIRCLE(x+10, y+10, radius, 'blue', startAngle, endAngle, 1.5); 
function CIRCLE (column, row, radius, color, startRadian, stopRadian, aspect) {
     var rotation = 0;
     var anticlockwise = 0;
       if (aspect == 1) {
        var rx = radius;
        var ry = radius;
     } else if(aspect < 1) {
        var rx = radius * aspect;
        var ry = radius;
     } else if(aspect > 1) {
        var rx = radius;
        var ry = radius * (aspect-1);
  }
    ctx.fillStyle=color;
  ctx.beginPath();
  ctx.ellipse(x, y, rx, ry, rotation, startAngle, endAngle, anticlockwise);
  ctx.fill();  
} 
<canvas id='can' width='200' height='150'></canvas>

Rectangles

In QuickBasic rectangles are drawn using lines. The syntax (according to QB64 Wiki) looks like:

LINE [STEP] [(column1, row1)]-[STEP] (column2, row2), color[, [{B|BF}]m style%]

Using the B option one can create an outlined box, using the coordinates specified as diagonal corners of the box. Using BF will create a filled box (e.g., with a color).