My Colorway Theme seems to be incomparable with the recent versions of PHP later than 7.0?

Hello

We have a website with the colorway pro theme and have recently experienced issues after updating PHP to a more recent version. We are unable to modify the theme options in "Appearance", just getting the message "The site is experiencing technical difficulties. Please check your site admin email inbox for instructions."
The email we receive details a number of PHP errors within the theme itself:
Error Details
=============
An error of type E_ERROR was caused in line 943 of the file /home/uhctcouk/public_html/wp-content/themes/colorwaytheme/functions/admin-interface.php. Error message: Uncaught Error: Call to undefined function ereg_replace() in /home/uhctcouk/public_html/wp-content/themes/colorwaytheme/functions/admin-interface.php:943
Stack trace:
#0 /home/uhctcouk/public_html/wp-content/themes/colorwaytheme/functions/admin-interface.php(125): optionsframework_machine(Array)
#1 /home/uhctcouk/public_html/wp-includes/class-wp-hook.php(286): optionsframework_options_page('')
#2 /home/uhctcouk/public_html/wp-includes/class-wp-hook.php(310): WP_Hook->apply_filters('', Array)
#3 /home/uhctcouk/public_html/wp-includes/plugin.php(465): WP_Hook->do_action(Array)
#4 /home/uhctcouk/public_html/wp-admin/admin.php(253): do_action('appearance_page...')
#5 /home/uhctcouk/public_html/wp-admin/themes.php(10): require_once('/home/uhctcouk/...')
#6 {main}
thrown
=========================================================

We now seem to get various php error warnings whichever version we use. PHP version 5.4 seems to function enough to allow us to edit the webpage, but anu other version blocks the options witht he above message preventing images and links being altered, particularly in the image slider at the top of the landing page. I suspect this may be the root of the issue.
Please can you help - is there any updates we can apply or that are pending? Our plugins seem to have no affect on these errors, with them still all occurring even with all plug ins disabled.
Thank you
Ol